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PAUL   B.HOEBEl 

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BY 

PERCY    G.    STILES 


Nutritional  Physiology 

i2ino  of   275  pages,   illustrated. 
Cloth,  $1.25  net. 


The  Nervous  System  and  Its 
Conservation 

i2mo  of   229  pages,  illustrated. 

jHSl   Out. 


THE  NERVOUS  SYSTEM 
AND  ITS  CONSERVATION 


BY 

PERCY  GOLDTHWAIT  STILES 

INSTRUCTOR  IN  PHYSIOLOGY  IN  HARVARD  UNIVERSITY  ; 
INSTRUCTOR  IN  PHYSIOLOGY  AND  PERSONAL  HYGIENE 
IN  THE  MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY  ; 
FORMERLY  ASSISTANT  PROFESSOR  OF  PHYSIOLOGY  IN 
SIMMONS    COLLEGE,    BOSTON 


ILLUSTRATED 


I 


PHILADELPHIA  AND  LONDON 

W.  B.  SAUNDERS   COMPANY 

1914 


Copyright,  1914,  by  W.  B.  Saunders  Company 


PRINTED     IN     AMERICA 

PRESS    OF 

W.    B.    SAUNDERS    COMPANY 

PHILADELPHIA 


TO 

EDITH  ARTHUR  BECKLER 

Co-worker  and  Friend: 

My  colleague  in  developing  the  instruction  in  Hygiene 

in  Simmons  College 


PREFACE 


There  are  several  excellent  books  devoted  to  the  anat- 
omy of  the  nervous  system,  there  are  others  which  treat 
of  its  physiology  in  an  illuminating  way,  and  others  still 
which  deal  with  its  hygiene.  If  the  present  volume  is 
not  to  be  an  impertinence,  it  must  be  justified  by  its 
attempt  to  combine  some  elements  of  the  three.  The 
intention  has  been  to  present  no  more  anatomy  than  is 
essential  to  an  appreciation  of  the  correlated  physiology 
and  to  subordinate  the  physiology,  in  its  turn,  to  the 
teaching  of  hygiene. 

In  the  chapters  which  deal  with  structure  and  func- 
tion the  writer  has  tried  to  gather  his  material  from 
authoritative  sources.  In  those  occupied  more  largely 
with  hygiene,  personal  judgments  have  doubtless  found 
expression.  But  the  desire  has  been  not  so  much  to 
dictate  in  a  dogmatic  spirit  as  to  open  important  mat- 
ters to  fuller  discussion. 

Many  associates  have  contributed  to  the  making  of 
this  book.  From  the  number  it  is  just  to  mention  Pro- 
fessor Ernest  G.  Martin,  of  Harvard,  whose  suggestions 
have  been  numerous  and  valuable. 

P.  G.  S. 
November,  1914 

7 


TABLE   OF  CONTENTS 


CHAPTER    I 
Introduction 

CHAPTER    II 

The  Minute  Structure  of  the   Nervous    Tissues 22 

CHAPTER    III 
The  Elements  of  Nerve  Physiology : .      36 


Reflexes  . 


CHAPTER    IV 

49 


CHAPTER    V 

The  General  Anatomy   of   the   Nervous  System 60 

CHAPTER    VI 

The  Afferent  Part  of  the  Nervous  System 75 

CHAPTER   VII 

The    Neuromuscular  Mechanism 85 

CHAPTER    VIII 

The  Neuromuscular  System:  Neuromuscular  Fatigue..    101 

CHAPTER    IX 

The  Autonomic    Nervous   System 114 

9 


10     ■  TABLK    OF    CONTENTS 

CHAPTER  X 

PACK 

The   Cerebrum l-~ 

CHAPTER    XI 
The  Cerebrum  and  Human   Development 142 

CHAPTER    Xn 

The  Cerebrum  and  the  Life   of   the   Individual 153 

CHAPTER    XIII 
Emotion. 164 

CHAPTER    XIV 
Sleep •. l^"^ 

CHAPTER    XV 
Dreams 184 

CHAPTER   XVI 

Causes  of   Nervous   Impairment 192 

CHAPTER    XVII 

Neurasthenia 203 

CHAPTER    XVIII 
Some  Matters  of  General   Hygiene 216 


Index  . 


225 


THE  NERVOUS  SYSTEM  AND  ITS 
CONSERVATION 


CHAPTER  I 
INTRODUCTION 

TISSUES 


Before  the  modern  microscope  was  available,  anato- 
mists and  physiologists  recognized  in  the  make-up  of  the 
human  body  various  types  of  constituent  substance  or 
fabric.  The  different  kinds  of  material  recognizable 
were  few  in  number  and  easily  assigned  to  certain  large 
classes.  Comparison  of  one  part  of  the  body  with  another 
showed  that  the  same  forms  of  organized  substance  were 
found  over  and  over  again.  The  several  varieties  of 
material  distinguished  came  to  be  known  as  tissues. 

In  the  hand,  for  example,  we  find  the  skin,  the  muscle, 
and  the  bone,  representatives  of  kinds  of  tissue  con- 
trasted in  function,  in  physical  character,  and  in  chemical 
composition.  Closer  study  of  the  hand  would  add  other 
members  to  the  list.  When  we  consider  the  tissues  with 
regard  to  the  intensity  of  the  life-processes  taking  place 
in  them  it  is  clear  that  this  is  anything  but  a  constant 
quantity.  In  some  cases  we  have  to  do  with  structures 
which  are  essentially  passive  in  their  nature  and  which 
might  conceivably  be  replaced  by  non-living  substitutes. 
This  is  true  of  those  tissues  which  are  described  as  con- 
nective. Their  service  is  mechanical;  they  unite  and  sup- 
port other  tissues.     Bone  is  a  conspicuous  example  of 

11 


12      THE    NERVOUS    SY8TK.M    AND    ITS    (X)\SKKVAT10N 

this  class,  and  very  much  as  the  skeleton  determines  the 
general  form  of  the  body,  so  each  organ  is  to  be  thought 
of  as  possessing  a  minor  framework  of  material  which 
behaves  for  the  most  part  as  though  it  were  not  really 
alive. 

It  is  usual  to  place  the  tissues  in  four  large  groups. 
Besides  the  connective,  to  whicli  reference  has  just  been 
made,  we  speak  of  the  epithelial,  the  muscular  or  con- 
tractile, and  the  nervous.  Epithelial  tissues  are  those 
which  form  surface  layers,  cither  internal  or  external. 
They  are  the  linings  and  the  coverings  of  the  organs. 
The  skin,  or  at  least  its  superficial  portion,  is  an  obvious 
example.  While  all  the  epithelia  answer  to  the  descrip- 
tion of  "coverings  or  linings,"  they  vary  widely  in  other 
respects.  Under  the  general  term  are  included  structures 
as  unlike  as  the  calloused  sole  of  the  foot,  the  exquisitely 
clear  cornea  of  the  eye,  and  the  excessively  thin  parti- 
tions interposed  between  the  blood  and  the  air  in  the 
lungs.  Judging  the  epithelial  tissues  by  their  share  in 
the  total  of  the  life-processes,  we  may  say  that  they  have 
both  passive  and  active  parts  to  perform.  In  some  places 
their  function  is  merely  protective;  in  others  they  have 
well-marked  chemical  activity.  Secretion  and  absorption 
are  epithelial  duties,  and  neither  the  one  nor  the  other 
could  be  carricfl  out  in  its  fulness  by  membranes  not 
living. 

Contractile  tissues  are  those  which  originate  the  move- 
ments of  the  parts  of  the  body.  Organized  into  large 
masses,  they  form  the  familiar  muscles.  The  heart  is 
mainly  composed  of  a  peculiar  contractile  material 
which  is  responsible  for  its  beating.  The  same  property 
is  manifested  by  elements  found  in  the  walls  of  the  ah- 
mentary  canal,  the  blood-vessels,  the  urinary  bladder, 
the  uterus,  and  other  hollow  viscera.  It  is  evident  that 
the  contractile  tissues  are  eminently  "alive" — that  no 
Hfeless  substances  could  be  expected  to  behave  as  they 
do.  Three  principal  varieties  are  recognized,  conveniently 
distinguished  as  the  skeletal,  the  cardiac,  and  the  visceral 


INTRODUCTION  13 

— names  which  go  far  to  denote  the  region  where  each  is 
discovered. 

The  nervous  tissues  are  far  less  conspicuous  in  an 
anatomic  sense  than  the  three  orders  just  enumerated. 
Let  us  imagine  for  a  moment  that  each  of  the  four 
divisions  in  which  we  have  placed  the  tissues  could  be 
presented  separately  to  view.  Four  human  figures  would 
appear  before  us.  That  one  composed  wholly  of  connect- 
ive tissue  would  consist  of  the  skeleton  as  a  basis,  and 
would  show,  in  addition,  an  indication  of  each  organ  in 
outline,  with  an  internal  system  of  interlacing  strands. 
It  would  include  the  ligaments  which  join  bone  with  bone, 
the  cartilages  which  also  occur  about  the  joints  as  well  as 
in  some  other  localities,  and  the  tendons  uniting  muscles 
with  bones.  The  muscles  themselves  would  be  blocked 
out  in  this  picture  by  the  surface  membranes  which  they 
possess  and  by  webs  of  non-contractile  material  within. 

The  second  figure  would  retain  the  complete  contour 
of  the  human  form,  inasmuch  as  it  would  have  the  skin. 
If  it  were  transparent  enough  the  cavities  and  external 
surfaces  of  the  viscera  would  be  seen  defined  in  their 
entirety,  but  with  spectral  lightness.  The  alimentary 
canal  would  be  traceable  as  a  winding  tube  of  great  deli- 
cacy within  another  still  more  diaphanous.  The  blood 
system  would  be  mapped  in  similar  fashion.  The  interior 
arrangement  of  each  gland  would  show  a  tree-like  pattern 
of  bewildering  intricacy. 

The  third  figure,  consisting  of  the  contractile  tissues, 
would  be  fragmentary  and  discontinuous.  To  conceive 
of  this  apparition  as  keeping  its  shape  calls  for  an  extra 
stretch  of  the  imagination.  It  would  supply  the  chief 
bulk  of  the  muscles  and  a  fraction,  missing  in  the  other 
manikins,  of  the  alimentary,  circulatory,  and  reproductive 
systems.  In  a  scattering  way  contractile  tissue  occurs 
even  in  the  skin,  where  its  presence  makes  possible  the 
"goose-flesh"  reaction.  Although  this  third  figure  would 
be  less  coherent  than  the  others,  it  would  greatly  exceed 
them  in  weight. 


14     .THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

What  would  remain  for  the  fourth  member  of  this 
uncanny  series?  It  has  been  reserved  for  a  reconstruc- 
tion of  the  nervous  tissues.  A  distant  view  of  it  woukl 
give  the  impression  of  a  ghostly  form  with  a  more  sub- 
stantial axis  expanding  above  into  a  bulbous  mass  in  the 
head.  On  closer  approach  the  axis  would  prove  to  be  the 
spinal  cord,  the  enlargement  above  would  be  recognized 
as  the  brain,  and  the  filmy  haze  which  completed  the 
figure  would  resolve  itself  into  many  nerves,  branching 
strands  proceeding  from  both  brain  and  cord  and  termin- 
ating in  a  cloud  of  finest  filaments.  These  filaments 
would  be  found  to  reach  almost  every  part  of  the  body 
(Fig.  1).  A  large  proportion  .would  be  seen  to  end  near 
the  external  surface;  a  great  many  could  be  followed  to 
localities  previously  determined  to  correspond  with  the 
skeletal  muscles;  still  others  would  be  manifestly  adapted 
to  make  connections  with  blood-vessels,  glands,  and  the 
contractile  elements  of  the  viscera. 

By  way  of  recapitulation  the  following  statements  may 
now  be  made:  The  human  body — or  the  bodj^  of  any 
animal  of  a  highl}''  organized  t^'pe — owes  its  relative 
constancy  of  form  to  an  inactive  supporting  system,  the 
connective  tissues.  It  owes  its  ability  to  move  to  the 
contractile  tissues.  The  epithelial  tissues  are  those  which 
establish  the  boundaries  between  the  organism  and  the 
environment;  through  them  exchanges  of  gaseous  and 
dissolved  substances  take  place.  The  service  of  the 
nervous  tissues  remains  to  be  indicated.  The  task  is  to 
occupy  us  throughout  the  present  volume.  But  a  con- 
densed preliminary  discussion  is  desirable. 

If  a  word  is  sought  which  shall  convey  a  general  idea 
of  the  work  of  the  nervous  system,  it  is  probable  that 
the  term  codrdinaiion  will  suggest  itself.  The  nerves 
serve  to  place  various  parts  of  the  body  in  communica- 
tion. This  statement  must  he  followed  at  once  with  the 
note  that  the  communication  afforded  is  never  directly 
from  organ  to  organ,  but  always  by  way  of  the  axial  part 
of  the  system.    Thus,  there  is  no  unbroken  nervous  high- 


INTRODUCTION 


15 


Fig.  1. — Diagram  illustrating  the  general  arrangement  of  the  nervous 
system  (Martin,  "The  Human  Body")- 


IG      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

way  from  the  stomach  to  the  heart,  nor  from  one  hand 
to  the  other.  Yet  the  stomach  may  influence  the  heart, 
the  central  part  of  the  mechanism  transmitting  the  effect. 
The  fundamental  plan  of  the  structure  involved  is  that  of 
a  tree,  and  just  as  an  ant  cannot  pass  from  one  of  the 
main  branches  to  another  without  visiting  the  trunk,  so 
all  physiologic  reactions  employ  a  central  link. 

Coordination  implies  order,  efficiency,  and  timeliness 
in  the  operation  of  a  machine.  These  desirable  qualities 
could  not  be  realized  in  the  living  machine  if  it  were  not 
for  the  nervous  system.  Coordination  is  akin  to  coopera- 
tion, and  the  purposeful  working  together  of  all  the  parts 
for  the  advantage  of  the  whole  is  accomplished  through 
the  aid  of  nerves  and  nerve-centers.  A  word  which  is  now 
frequently  heard  in  this  connection  is  integratio?!.  The 
nervous  system  may  be  said  to  confer  integrity  upon  the 
organism.  This  is  to  say  that  the  unity  or  oneness  of  the 
animal  is  almost  wholly  dependent  upon  this  feature. 
It  is  not  entirely  so,  for  we  are  realizing  more  and  more 
that  chemical  products  passing  from  organ  to  organ  have 
much  to  do  with  the  coordinating  of  activities.  If  the 
nervous  tissues  could  be  instantly  eliminated  from  the 
body  of  a  dog  without  doing  other  injury,  the  life  proc- 
esses would  not  immediately  cease,  but  they  would  be- 
come local  and  partial.  They  could  no  longer  be  com- 
bined to  the  advantage  of  the  animal.  The  nervous  sys- 
tem confers  upon  the  associated  tissues  the  right  to  rank 
as  an  individual. 

It  is  scarcely  possible  to  use  the  word  "individual" 
without  introducing  the  idea  of  a  self-conscious  being. 
One's  own  nervous  system  is,  in  part,  demonstrated  to 
one  through  personal  consciousness.  This  is  the  field  of 
psychology.  The  physiologist  is  more  properly  a  student 
of  the  objective  than  the  subjective,  and  he  is  occupied 
for  the  most  part  with  observing  the  reactions  mediated 
by  nervous  systems  other  than  his  own.  Yet  it  may  be 
claimed  that  there  is  a  considerable  borderland  common 
to  the  two  branches  of  science  within  which  it  behooves 


INTRODUCTION  17 

both  the  psychologist  and  the  physiologist  to  make 
ventures.  It  is  fortunate,  nevertheless,  that  a  great  many 
facts  can  be  noted  and  discussed  without  any  reference  to 
supposed  mental  states  in  animals. 

We  can  deal  with  all  the  reactions  brought  about 
through  the  nerve-centers  in  the  simpler  animals  without 
assuming  psychic  accompaniments,  and  the  same  method 
carries  us  very  far  with  our  attempted  analysis  of  nerve 
physiology  in  the  higher  forms.  A  man  cannot  regard 
his  own  brain  in  quite  the  same  way  in  which  he  regards 
his  liver,  but  when  he  is  bent  on  studying  the  hving  nervous 
system  in  a  frog,  a  cat,  or  even  in  another  human  being 
his  immediate  concern  is  with  what  it  does — not  with  what 
is  felt  while  the  action  is  in  progress.  Eventually  he  is 
obliged  to  consider  sensation  in  connection  with  his  other 
problems,  but  it  is  well  to  defer  as  long  as  possible  the 
admission  of  psychologic  elements. 

In  accordance  with  what  has  been  said,  an  objective 
treatment  of  the  nervous  system  will  be  pursued  for  the 
present.  The  nerves  will  be  looked  upon  as  conductors 
of  energy.  The  chief  source  of  this  energy  will  be  recog- 
nized in  the  external  forces  which  are  brought  to  bear 
upon  the  organism  and  which  are  termed  stimuli.  The 
destination  of  the  currents  of  energy  will  be  found  in  the 
contractile  and  secreting  tissues  whose  activities  they 
modify.  Life  that  is  not  one's  own  is  manifested  through 
movement,  heat  production,  and  secretion;  it  is  very 
rarely  that  we  are  obliged  to  take  other  responses  into 
account.  Attention  must  be  directed  to  the  fact  that 
nervous  tissues  separated  from  others  can  scarcely  give 
clear  evidence  of  their  internal  changes.  Muscles  and 
glands  are  required  to  testify  to  what  is  passing  in  the 
governing  mechanism.  (Except  for  certain  electric  symp- 
toms of  very  slight  intensity  we  should  not  be  able  to 
decide  whether  a  detached  portion  of  a  nerve-trunk  were 
living  or  lifeless.) 


IS      THIO    NERVOUS   SYSTKM    AND    ITS    CONSIOKVATIOX 

RECEPTORS;  ADJUSTORS;  EFFECTORS 

These  three  words  have  recentl}^  l)een  used  to  develop 
a  most  simple  and  helpful  outline  of  the  general  work 
of  the  nervous  system.  Whether  we  consider  a  worm,  an 
ins6ct,  a  reptile,  or  a  mammal,  three  departments  of 
orp;anization  with  functions  of  three  orders  can  be  indi- 
cated. The  receptors,  as  the  name  implies,  constitute 
that  department  of  the  system  which  is  subject  to  ex- 
ternal influences.  Receptors  are  wrought  upon  by  press- 
ure, by  changes  of  temperature,  by  chemical  agents  in 
solution.  In  the  more  highly  developed  animals  they 
include  particular  sense  organs  like  the  eye  and  the  ear. 
Such  organs  translate  vibratory  energy  of  the  ether  and 
the  air  respectively  into  the  form  of  energy  which  nerves 
convey. 

It  is  to  be  noted  that  receptors  may  be  strictly  part 
of  the  nervous  system,  as  where  naked  endings  of  the 
fibers  lie  exposed  to  contacts,  or  they  may  be  mechanisms 
made  of  other  tissues  serving  to  transmute  and  apply  the 
energy  of  the  stimulus.  Where  the  receptor  does  not  con- 
stitute a  part  of  the  nervous  sj^stem  the  path  from  it  to 
the  central  axis  must  be  given  a  special  name,  and  it  is 
spoken  of  as  a  sensory  or  afferent  path. 

The  effectors  upon  which  the  nervous  system  plays 
include  the  contractile  and  glandular  tissues.  The  effec- 
tors are  always  distinct  from  the  nervous  system,  and  the 
fibers  stretching  out  to  them  form  efferent  paths.  The 
third  class  of  working  units,  the  adjustors,  are  those 
within  the  nervous  sj^stera  which  mediate  between  the 
receptors  and  the  effectors,  or,  more  accurately,  between 
afferent  and  efferent  pathways.  It  is  in  the  realm  of  the 
adjustors  that  the  utmost  complexity  of  organization  is 
possible.  The  variety  of  reaction  so  typical  of  animals 
which  we  call  "high  in  the  scale"  has  its  physical  basis  here. 

Parker,^  of  Harvard,  has  written  most  suggestively  of 

1  G.  H.  Parker,  "The  Origin  and  Significance  of  the  Primitive 
Nervous  System,"  Proceedings  of  the  American  Philosophical 
Society,  1911,  vol.  1,  No.  199. 


INTRODUCTION  19 

the  probable  sequence  in  which  the  three  orders  of  elements 
have  acquired  their  position  in  relation  to  the  nervous 
system  of  standard  type.  According  to  his  hypothesis 
there  may  have  been  a  certain  lowly  condition — possibly 
reahzed  in  sponges — in  which  contractility  was  displayed 
only  in  response  to  distinct  and  direct  stimulation  brought 
to  bear  from  the  outside  world  upon  tissues  having  the 
power  of  movement.  No  separate  and  definitely  nervous 
tissue  would  be  requisite  to  apply  the  stimuh,  but  if  such 
a  transmitter  should  be  evolved  it  would  be  evident  that 
an  efferent  element  had  come  into  existence.  Parker  thus 
conjectures  that  the  efferent  is  the  most  primitive  feature 
of  the  three. 

In  the  course  of  development  the  submergence  of  the 
contractile  tissues  below  the  exposed  surface  of  the  body 
would  make  it  necessary  that  a  receptor  should  be  added. 
Its  function  would  be  to  maintain  relations  between  the 
exterior  and  the  hidden  effector.  One  receptor  joined  with 
one  effector  would  form  a  sufficient  means  for  bringing 
about  one,  and  only  one,  reaction.  The  arrangement 
does  not  admit  of  any  flexibility.  It  is  the  simplest  ex- 
ample of  what  is  called  a  reflex  arc.  With  the  addition  of 
intermediate  links  between  the  receptor  and  the  effector 
departments  the  reaction  becomes  less  and  less  predictable. 
This  is  equivalent  to  saying  that  it  becomes  more  and 
more  like  the  actions  of  the  higher  animals — subject  to 
reinforcement,  suppression,  or  modification  under  the 
influence  of  changing  circumstances.  Many  illustrations 
will  be  given  later  which  will  serve  to  clear  up  this  matter. 

Excitation  and  Inhibition. — The  common  conception 
of  the  function  of  nerves  is  that  they  arouse  activity. 
This  is  essentially  true  of  those  which  stretch  out  from 
the  central  axis  to  the  skeletal  muscles,  and  which  call 
forth  the  evident  movements  of  the  limbs,  the  play  of 
facial  expression,  etc.  The  muscles  involved  in  such  move- 
ments are  relaxed  and  paralyzed  when  their  nervous  con- 
nections are  interrupted.  It  is  because  this  fact  is  so 
prominent  that  one  may  easily  fall  into  the  error  of  sup- 


20      THE    NERVOUS    SYSTEM   AND    ITS    CONSERVATION 

posing  that  no  process  of  contraction  or  secretion  takes 
place  save  as  the  nervous  system  initiates  it.  This  is  very 
far  from  being  the  case. 

All  the  branches  of  the  nerves  which  enter  the  substance 
of  the  heart  may  be  cut,  but  the  heart  will  continue  to 
beat.  Hence,  we  cannot  beheve  that  each  beat  of  the 
heart  is  dictated  by  the  efferent  elements  of  the  coordinat- 
ing system.  The  power  to  make  rhj^thmic  contractions 
is  resident  in  the  organ  itself;  we  say  that  it  is  automatic. 
In  a  less  striking,  but  still  positive,  way  other  organs  dis- 
play a  tendency  to  activity  when  removed  from  central 
command.  This  is  demonstrable  for  the  stomach,  the 
intestine,  and  the  urinar}'  bladder.  The  contractile  tis- 
sues which  enter  into  the  make-up  of  these  viscera  must 
be  said  to  have  a  degree  of  automaticity. 

When  an  organ  has  this  disposition  to  be  active  on  its 
own  account  it  will  be  seen  that  the  nervous  sj^stem  may 
exert  a  twofold  influence  upon  it.  The  native,  local 
process  may  be  accelerated  beyond  its  average  rate  of 
progress,  or  it  may  be  restrained  more  or  less  radically. 
We  say  that  tissues  which  possess  the  automatic  property 
may  exhibit  either  excitation  or  inhibition  when  the  nervous 
system  modifies  their  inherent  tendency.  It  is  probably 
just  to  claim  that  both  with  the  heart  and  with  the  alimen- 
tary tract  inhibitory  effects  are  more  frequently  witnessed 
than  are  those  which  are  clearly  excitatory.  If  one  is 
incHned  to  cjuestion  this,  on  the  ground  that  quickening 
of  the  heart-beat  in  exercise  is  a  daily  experience,  it  may 
be  answered  that  this  quickening  is  known  to  be  to  a 
great  extent  the  withdrawal  of  an  inhibition  previously 
operative.  Withdrawal  of  inhibition  is  a  form  of  counter- 
feit stimulation  which  will  repeatedly  call  for  considera- 
tion in  later  paragraphs.  The  slowing  of  the  heart  after 
exercise  may  be  a  more  positive  instance  of  nervous  inter- 
vention than  the  hastening  of  its  action,  which  seems  so 
much  more  impressive. 

As  for  the  alimentary  canal,  it  lias  become  well  recog- 
nized that  its  movements  are  actually  observed  to  better 


INTRODUCTION  21 

advantage  when  it  is  removed  from  the  reach  of  central 
influences  than  when  its  nervous  connections  are  intact. 
It  is  not  unhkely  that  there  are  a  good  many  human 
beings  suffering  from  indigestion  of  nervous  origin  who 
would  have  less  trouble  if  their  stomachs  and  intestines 
could  be  placed  quite  out  of  reach  of  brain  and  cord  and 
left  to  work  as  determined  by  their  own  intrinsic  proper- 
ties. According  to  this  view,  suspension  of  the  motor 
activities  of  the  canal  is  a  possibility  easily  realized. 
Acceleration  may  also  be  effected,  but  cannot  be  held  to 
be  so  common  and  striking  an  occurrence. 

When  the  first  clear  instance  of  inhibition — the  case  of 
the  heart — was  brought  to  the  attention  of  scientists  in 
the  year  1845  it  was  received  with  surprise  and,  at  first, 
with  increduhty.  All  sorts  of  explanations  were  offered 
for  the  phenomenon,  with  the  intention  of  proving  that 
it  was  not  a  true  suppression  of  activity.  In  course  of 
time,  however,  inhibition  had  to  be  recognized  as  a  power 
of  the  nervous  system  fully  as  direct  and  characteristic 
as  excitation.  It  is  now  fair  to  say,  as  a  concise  statement 
of  all  which  has  gone  before,  that  the  duty  of  the  nervous 
system  is  to  translate  the  energy  of  external  stimulation 
into  nerve-impulses,  to  carry  these  to  the  central  axis,  and 
to  apply  them  through  the  efferent  paths  either  to  arouse 
or  to  restrain  the  action  of  the  contractile  and  secreting 
tissues.  The  nature  of  the  energy  which  is  transmitted 
along  the  nerves  can  best  be  discussed  after  we  shall  have 
obtained  some  insight  into  the  microscopic  organization 
of  the  nervous  mechanism. 


CHAPTER   II 

THE    MINUTE    STRUCTURE    OF    THE    NERVOUS 
TISSUES 

Our  Introduction  began  with  references  to  the  existence 
of  a  few  tj^pes  of  tissue  in  the  human  body.  These  types 
have  been  famiUar  to  anatomists  for  more  than  a  century. 
A  large  share  of  the  credit  for  their  recognition  and 
definition  belongs  to  Bichat,  a  French  worker,  whose 
short  life  of  only  thirty  years  (1771-1801)  was  extra- 
ordinary for  the  extent  of  its  achievements.  Forty  years 
after  the  death  of  Bichat  an  important  step  had  been 
taken  toward  a  more  comprehensive  knowledge  of  the 
way  in  which  living  matter  is  constructed.  The  doc- 
trine declared  at  that  time  is  known  as  the  Cell  Theory. 
Its  estabhshment  was  directly  due  to  a  noteworthy  im- 
provement in  the  lenses  made  for  microscopes. 

The  Cell  Theory  is  to  the  effect  that  all  forms  of  life  can 
be  demonstrated  to  exist  as  single  or  associated  units  of  a 
certain  standard  kind.  These  units  of  structure  continue 
to  bear  the  name  of  cells,  though  the  word  became  fixed 
upon  them  at  first  as  the  result  of  a  misconception.  It 
is  not  logical  to  use  a  word  which  properly  means  a  cavity 
to  stand  for  a  more  or  less  solid  mass  of  material,  but  this 
is  the  actual  practice.  The  biologic  cell  may  be  regarded 
as  having  the  same  relation  to  a  cell  in  the  precise  sense 
of  the  term  that  a  cast  has  to  the  mold.  In  short,  the  cell 
is  a  small  parcel  of  living  matter,  the  smallest  which  can 
continue  long  to  have  the  behavior  which  we  associate 
with  the  living  state. 

An  average  cell  is  microscopic  in  size.  Many  of  those 
in  the  body  would  be  found  to  measure  less  than  j  oVcr  iiich 
in  diameter;  the  red  corpuscles  of  the  blood,  for  example, 

22 


MINUTE    STRUCTURE   OF   THE    NERVOUS    TISSUES      23 

are  only  32-V^  ^^'^^  across  their  circular  faces.  If  there  can 
be  said  to  be  a  standard  of  form  for  the  cell,  it  is  the 
sphere.  But  this  primitive  form  is  merely  the  point  of 
departure  for  the  widest  variations.  The  units  in  con- 
tractile tissues  are  always  greatly  elongated,  those  of  epi- 
thelia  are  flattened,  cubic,  or  prismatic,  those  of  connective 
tissue  are  irregular  and  often  quite  freely  branched.     The 


Fig.  2. — Drawings  like  the  above  are  almost  always  made  from 
tissues  which  have  been  prepared  and  colored  by  special  means  to 
make  clear,  minute  features,  a  represents  an  ovum  or  egg-cell, 
the  typical  cell  may  be  assumed  to  tend  toward  this  spheric  form; 
6  is  a  cell  from  a  compact  tissue,  to  show  how  mutual  pressure  pro- 
duces a  faceted  or  polyhedral  form;  c  is  a  contractile  element  such 
as  occurs  in  the  walls  of  the  alimentary  canal,  it  illustrates  an  elon- 
gated cell;  d  is  an  epithelial  or  lining  cell  of  the  order  found  on  the 
inner  surface  of  blood-vessels;  this  is  an  example  of  extreme  fatten- 
ing; e,  from  the  nervous  system,  exhibits  the  possibility  of  a  branch- 
ing development. 

cells  in  nervous  tissues  are  most  peculiar  of  all,  and  must 
presently  be  described  at  some  length  (Fig.  2). 

When  such  diversity  of  form  is  considered  the  student  is 
disposed  to  ask:  What  have  these  differing  packets  of 
organized  substance  in  common  that  the  same  name 
should  be  applied  to  them  all?  It  is  hard  to  say  that 
any  single  feature  is  always  to  be  found  in  them.     One 


24      THE    NERVOUS    SYSTEM    AXD    ITS    CONSERVATION 

which  is  prominent  in  the  great  majority  is  the  nucleus. 
This  is  a  body  within  the  cell,  seemingly  more  dense  than 
the  remainder  and  unlike  the  rest  in  its  chemical  character. 
The  last  fact  is  proved  by  the  individual  reactions  of  the 
nucleus  toward  selected  stains  or  dyes.  When  tissues 
are  treated  with  such  solutions,  the  nucleus,  which  maj' 
have  been  quite  invisible  in  the  uncolored  specimen, 
appropriates  the  stain  and  stands  out  in  .striking  contrast 
to  the  pale  substance  which  envelops  it.  Excepti(nially 
there  may  be  more  than  one  nucleus  to  a  cell  or,  again, 
none  may  be  discernible.  Cells  are  said  to  be  composed 
of  protoplasm,  and  the  word  is  often  used  as  synonymous 
with  living  matter.  Huxley  called  it  the  physical  basis  of 
life.  The  particular  word  cytoplasm  will  be  found  useful 
to  designate  the  portion  of  the  cell  which  is  external  to 
the  nucleus. 

The  statement  that  tissues  are  composed  of  cells  is 
open  to  some  objection.  Tissues  are  made  by  cells,  but 
in  the  course  of  their  development  they  commonly  come 
to  contain  material  of  a  sort  which  cannot  be  described 
as  cellular.  Such  material  is  conveniently  termed  "inter- 
cellular substance"  and  it  is  probably  alwaj^s  lifeless. 
Sometimes  it  is  scarcely  recognizable,  while  at  the  other 
extreme  it  may  be  so  abundant  as  to  constitute  the  main 
bulk  of  the  tissue  and  to  determine  its  physical  properties 
and  its  value  to  the  animal.  Thus,  bone  is  serviceable 
because  of  the  intercellular  lime  salts  which  give  it  rigid- 
ity. The  cells  have  come  to  occupy  a  very  inconspicuous 
position,  and  though  they  continue  to  exert  a  needed 
influence  upon  nutrition,  they  are  not  at  all  concerned 
from  moment  to  moment  in  the  mechanical  function 
fulfilled  by  the  bone  as  a  part  of  the  skeleton.  All  con- 
nective tissue  is  distinguished  by  the  high  proportion  of 
intercellular  substance  contained  in  it.  The  clear,  glassy 
concrete  of  cartilage,  the  tough,  white  fibers  in  tendons 
and  ligaments,  the  network  between  the  skin  and  the 
muscles — these  are  examples  of  material  which  is  not  made 
of  cells,  though  it  was  made  hy  them. 


MINUTE    STRUCTURE    OF   THE    NERVOUS   TISSUES      25 

It  has  proved  far  more  difficult  to  gain  a  satisfactory 
knowledge  of  the  intimate  structure  of  the  nervous  system 
than  to  master  the  minute  plan  of  other  tissues.  Students 
at  the  present  time  are  by  no  means  agreed  in  their  inter- 
pretation. Fortunately,  even  an  imperfect  picture  of  the 
microscopic  arrangement  throws  much  light  upon  the 
physiologic  processes  observed.  From  one  point  of  view 
it  may  be  claimed  that  the  chief  office  of  the  nervous 
system  is  conduction.  We  shall  do  well  to  attend  first  to 
the  elements  which  are  known  to  carry  on  this  particular 
duty.  These  elements  are  the  nerve-fibers;  collected  in 
bundles  they  make  the  nerves. 

A  nerve  is  usually  assumed  to  be  a  strand  directly  or 
indirectly  connected  with  the  central  system  and  large 
enough  to  be  followed  by  the  naked  eye  as  the  body  is 
dissected.  The  fiber  is  too  small  to  be  traced  in  this  way. 
Fibers  bear  a  relation  to  nerves  like  that  which  wires 
bear  to  cables  in  which  they  are  bound  up.  It  follows 
that  the  number  of  the  nerves  is  of  a  moderate  order,  while 
that  of  the  fibers  is  expressed  in  millions.^  Nerves  are 
often  seen  to  subdivide,  but  when  such  branching  occurs 
the  fibers  are  merely  assorted;  they  do  not  fork  where  the 
nerve  does,  but  are  found  in  equal  numbers  in  the  trunk 
and  in  the  sum  of  its  branches.  This  does  not  mean  that 
nerve-fibers  never  do  subdivide,  for  there  are  important 
instances  of  such  behavior,  but  subdivision  is  usually 
met  with  either  in  the  central  axis  or  near  terminal 
structures  rather  than  in  the  nerve-trunks  (Fig.  3). 

A  nerve-fiber  consists  of  a  core  surrounded  by  one  or 
two  sheaths.  The  double  covering  is  the  more  common 
arrangement,  at  least  outside  the  brain  and  cord.  The 
suggestion  of  an  insulated  wire  is  strong.  Here,  as  in  the 
wire,  it  is  certainly  the  core  which  is  the  essential  con- 
ductor; the  sheaths  can  scarcely  be  regarded  as  insulating 
material  in  the  ordinary  meaning  of  the  word,  but  they 
are  rather  calculated  to  support  and  nourish  the  axis- 

1  Between  3,000,000  and  4,000,000  has  been  estimated.  Donald- 
son, "The  Growth  of  the  Brain,"  Scott,  London,  1895,  p.  196. 


2G      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

cijlimler  or  axon,  as  the  enclosed  transmitter  is  called. 
Investigation  bj'^  refined  methods  has  made  it  probable 
that  the  axon  can  be  resolved  into  a  number  of  very  small 
fil^rils.  The  idea  that  there  may  be  conducting  units 
finer  and  more  numerous  than  the  fibers  as  usually  recog- 
nized opens  interesting  possibilities. 

The  protective  sheaths  are  broken  into  segments  at 
intervals  of'a  millimeter  or  less  and  thus  present  a  jointed 
arrangement.  These  joints  are  known  as  the  nodes  of 
Ranvier,  and  the  fact  is  to  be  emphasized  that  they  do  not 
interrupt  the  continuity  of  the  axis-cyhnder.  This  goes 
on  unbroken  like  the  thread  in  a  necklace.  Nerve-fibers 
attain  a  great  length;  the  longest  are  not  much  shorter 


Fig.  3. — Two  nerve-fibers  shown  diagrammatically  especially 
to  emphasize  the  continuity  of  the  axon.  A  detail,  further  enlarged, 
to  suggest  tibrils  in  the  axon. 

than  the  entire  body.  They  may  in  other  eases  be  so 
short  as  hardly  to  pass  outside  a  single  microscopic  field. 
We  must  now  consider  the  manner  of  their  beginnings 
and  endings. 

In  studying  the  nervous  tissues  without  the  aid  of  the 
microscope  anatomists  long  ago  began  to  refer  to  two 
types  which  they  called  respectively  gray  and  white 
matter.  Most  of  the  nerve-trunks  can  be  decisively  classi- 
fied as  white  matter,  and  when  we  find  substance  of  a 
similar  appearance  in  the  cord  or  the  brain  we  may  con- 
clude that  its  organization  is  much  the  same  as  that  of  the 
ordinary  nerves.  We  have  already  seen  that  nerves  are 
bundles  of  fibers  laid  closely  together  and  having  a  parallel 
direction.    The  microscope  shows  that  this  is  equally  the 


MINUTE    STRUCTURE    OF    THE    NERVOUS    TISSUES      27 

case  with  other  white  matter.    It  is  always  and  exclusively 
devoted  to  conduction. 

Gray  matter  is  far  more  intricate  in  structure  and  its 
physiology  is  less  easily  defined.  It  is  massed  for  the  most 
part  in  the  central  nervous  system.  Small  detached  col- 
lections, the  ganglia,  exist  in  other  localities.  An  inspec- 
tion of  typical  gray  matter  gives,  first  of  all,  the  impression 
of  looseness  of  texture.  Nerve-fibers  are  seen  straying 
through  the  field,  but  never  in  a  compact  formation. 
Attention  is  quickly  attracted  by  the  curious  bodies  which 


Fig.  4. — A  common  type  of  nerve-cell  (or  perikaryon)  giving  rise 
to  the  axon  of  a  nerve-fiber. 

are  most  characteristic  of  this  tissue,  the  so-called  nerve- 
cells.  These  vary  widely  in  size,  but  probably  have,  on 
the  average,  about  the  same  dimensions  as  other  cells. 
In  each  one  a  conspicuous  nucleus  can  be  demonstrated. 
But  the  most  remarkable  features  of  most  nerve-cells 
are  the  numerous  processes  which  extend  from  them 
(Fig.  4). 

It  has  been  said  that  the  cells  in  connective  tissue  some- 
times show  a  highly  irregular  outline.  The  cells  of  the 
nervous  system,  however,  surpass  all  others  in  this  re- 
spect.   Their  protoplasm  is  spun  out  into  prolongations 


28      THE    Xi:iiV()U«    SYSTEM    AXD    ITS    CONSERVATION 

which  become  more  aiul  more  slender  as  they  branch  until 
their  ultimate  subdivisions  defy  observation.  Each  nerve- 
cell,  as  a  rule,  has  manj'^  of  these  brush-like  extensions, 
and  since  other  cells  are  near  at  hand  the  processes  inter- 
lace in  a  bewildorino;  fashion.  A  recent  writer  has  likened 
the  resulting  situation  to  that  prevailing  in  a  forest  where 
the  branches  of  each  tree  penetrate  among  those  of  its 
neighbors.  Looking  among  the  foliage  from  a  little  dis- 
tance one  cannot  tell  to  which  tree  individual  twigs  belong. 

Keeping  for  the  moment  the  illustration  just  introduced, 
it  may  be  said  that  the  observer  could  hardly  tell  whether 
the  ends  of  the  small  branches  ended  freely  or  ran  together. 
His  information  would  enable  him  to  decide  that  each 
tree  is  really  quite  without  connection  with  any  other, 
but  he  might  not  be  able  to  determine  this  by  his  distant 
inspection.  This  represents  with  entire  justice  the  diffi- 
culties encountered  by  workers  who  have  tried  to  inter- 
pret the  appearance  of  the  gray  matter.  They  have  not 
been  able  to  agree  as  to  whether  the  processes  of  one  nerve- 
cell  are  continuous  with  those  of  others  or  whether  they 
merely  mingle  closely.  Fortunately,  the  physiologj^  of 
the  nervous  tissues  can  be  discussed  without  the  adoption 
of  one  view  to  the  exclusion  of  the  other.  The  prime  fact 
has  to  be  accepted  that  effects  are  produced  by  certain 
cells  upon  their  neighbors. 

A  term  which  it  is  most  important  to  understand  is 
synapse.  A  synapse  is  said  to  exist  wherever  the  branch- 
ing processes  of  a  nerve-cell  transmit  stimulating  energy 
to  the  processes  of  a  second  unit.  If  there  is  no  con- 
tinuity between  the  two,  the  synapse  is  a  place  of  contact 
or  of  close  approach.  If  the  adjacent  units  of  the  gray 
matter  are  really  bound  together,  the  sjaiapse  is  the  region 
of  the  finest  subdivision  of  the  protoplasmic  bonds  between 
them.  If  we  speak  physiologically,  the  synapse  is  a 
functional  junction;  it  is  not  absolutely  necessary  to 
decide  whether  it  is  an  anatomic  junction.  One  doctrine 
implicitly  held  with  reference  to  the  synapse  is  that  trans- 
mission across  it  can  take  place  in  only  one  direction. 


MINUTE    STRUCTURE    OF   THE   NERVOUS    TISSUES      29 

The  property  involved  has  been  spoken  of  as  a  "valve- 
action"  (Fig.  5). 

Most  of  the  processes  which  spring  from  nerve-cells 
are  of  the  branching  character  which  has  been  described. 
They  are  called  dendrites  or  dendrons.  But  certain  proc- 
esses are  found  to  be  of  an  entirely  different  order.  These 
can  be  followed  often  for  long  distances  from  the  cells 
which  give  rise  to  them,  and  are  presently  found  to 
acquire  the  sheaths  previously  mentioned  as  enveloping 
the  axis-cylinders  of  nerve-fibers.  Just  here  we  reach 
a  most  fundamental  conclusion  as  regards  the  constitu- 
tion of  the  nervous  system:  that  each  nerve-fiber — or, 


Fig.  5. — To  illustrate  a  synapse  (S),  which  is  the  functional 
junction  between  the  terminal  arborizations — i.  e.,  fine  branchings — 
of  the  left-hand  neuron  and  certain  dendrites  of  the  one  to  the  right. 
Effects  are  secured  only  in  the  du-ection  of  the  arrows. 

more  accurately,  its  central  core — is  the  outgrowth  of  a 
nerve-cell.  This  defines  the  relations  existing  between 
the  gray  and  the  white  matter.  In  the  gray  matter  are 
the  cell-bodies;  in  the  white  matter  run  their  long  proc- 
esses, the  conductors  of  energy  in  the  form  which  we  have 
called  nerve-impulses.  However  far  nerve-fibers  may 
stretch  from  the  situation  of  their  presiding  cells,  their 
axons  are  to  be  recognized  as  continuous  with  the  proto- 
plasm of  those  microscopic  elements.  The  axon  in  a 
long  fiber  may  contain  many  times  as  much  substance  as 
the  cell-body  in  which  it  originates. 

A  question  of  terminology  now  arises.  If  the  axis- 
cyhnder  is  part  and  parcel  of  the  structural  unit  which 


30      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

has  it;?  nucleus  in  the  gray  matter,  do  we  do  well  to  call 
the  portion  about  the  nucleus  the  cell  and  to  imply  that 
the  core  of  the  fiber  is  not  to  be  reckoned  as  belonging  to 
it?  It  is  reasona])lc  to  claim  that  the  cell  should  he  held 
to  include  all  its  extensions,  no  matter  how  prolonoed. 
Histologists  have  appreciated  the  force  of  this  argument 
and  have  proposed  words  to  denote  more  precisely  the 
features  under  discussion.  What  we  have  generally  called 
the  nerve-cell  may  better  be  called  the  perikaryon,  which 
means  specifically  "around  the  nucleus."  When  we 
adopt  this  we  find  ourselves  in  need  of  a  word  for  the 
combination  of  perikaryon,  dendrites,  and  axon  (or 
axons) — in  short,  for  the  nerve-cell  in  the  best  sense. 
The  word  supplied  is  neuron. 

The  Neuron  Theory. — It  is  now  time  to  outline  the 
conception  of  tlie  anatomy  and  physiology  of  the  nervous 
system  which  for  twenty-five  years  has  been  the  founda- 
tion of  most  presentations  of  these  subjects.  To  do  this 
will  be,  in  part,  to  restate  what  has  gone  before,  but  we 
shall  be  led  also  to  fresh  considerations.  The  ideas  to  be 
explained  are  not  to  be  received  as  surely  demonstrated, 
but  they  have  probably  not  seriously  misled  students  in 
the  past,  however  they  may  have  to  be  modified  in  the 
future.  New  views  are  now  urged  by  many  skilled  in- 
vestigators and  we  must  not  ignore  them.  Nevertheless, 
the  traditional  picture  of  the  nervous  elements  and  their 
relationships  remains  convenient  for  teaching  and  diagram- 
matic purposes. 

The  neuron  theory  assumes  that  the  whole  system  is 
capable  of  resolution  into  highly  specialized  cells  of  the 
nature  already  indicated.  These  neurons  are  said  to  be 
"concatenated,"  which  means  enchained.  The  indi- 
vidual neuron  is  commonly  supposed  not  to  be  continuous 
with  any  of  its  fellows,  but  it  is  supposed  to  affect  and  to 
be  affected  by  them  through  synapses.  The  valve  action 
emphasized  above  gives  each  neuron  a  certain  regularity 
of  performance ;  it  can  receive  stimuli  at  certain  points,  but 
it  cannot  communicate  them  at  the  same  places.    So  also 


MINUTE    STRUCTURE    OF   THE    NERVOUS   TISSUES      'SI 

it  can  despatch  impulses  to  other  neurons,  but  they  cannot 
react  upon  it.  What  follows  is  most  important :  axons  are 
nearly  always  channels  for  the  conveyance  of  impulses 
away  from  the  perikaryon — dendrites  are  receptive  in 
function.  It  is  probably  a  fact  that  the  majority  of  neu- 
rons are  of  the  type  having  numerous  dendrites  and  only 
one  axon.  The  arrangement  makes  stimulation  from  many 
directions  a  possibility,  but  gives  a  fixed  course  to  the 
resulting  outflow  of  energy.  Vast  numbers  of  neurons 
are  to  be  found  in  the  central  gray  matter  which  have 
only  short  processes  and  which  do  not  easily  admit  of 
distinguishing  dendrites  from  axons,  yet  the  distinction 
is  assumed. 


Fig.  6. — To  show  how  in  an  afferent  neuron  the  transmission  is 
from  the  endings  subject  to  stimulation  (i?)  to  a  synapse  (S)  in  the 
central  nervous  system.  The  perikaryon  has  an  intermediate  posi- 
tion and  its  functions  other  than  that  of  maintenance  are  problem- 
atic. 

One  kind  of  neuron  stands  somewhat  in  contrast  with 
all  the  other  varieties,  inasmuch  as  it  has  a  smooth  peri- 
karyon without  sign  of  dendrities.  A  single  axon  runs 
for  a  short  distance  away  from  the  perikaryon  and  is  then 
found  to  fork  and  to  be  traceable  for  a  long  waj^  in  either 
direction.  This  type  of  unit  is  peculiar  to  the  afferent 
department  of  the  nervous  system.  It  is  marked  physio- 
logically by  the  fact  that  it  is  not  adapted  to  be  stimulated 
by  other  neurons,  but  by  energies  acting  from  sources 
external  to  the  nervous  mechanism.  In  such  a  neuron 
the  perikaryon  is  usually  buried  far  from  the  normal 
operation  of  external  stimuli.  If  it  bore  the  ordinary 
short  dendrites  and  lay  open  to  stimulation  within  the 


32      TH1-:    NERVOUS   SYSTEM    A.\U    ITS   CONSERVATION 

gray  matter,  this  could  only  result  in  confusion  of 
reaction  and,  in  case  sensations  were  aroused,  in 
hallucinations.  This  assertion  can  be  justified  later 
(Fig.  G). 

Let  us  consider  in  what  various  ways  nerve-fibers 
may  terminate.  Those  which  serve  the  receptors  are 
called  afferent,  those  which  act  on  effectors  are  said  to  be 
efferent.  Most  afferent  fibers  are  parts  of  neurons  like 
those  described  in  the  paragraph  above;  the  perikaryon 
in  each  one  is  neither  at  the  beginning  nor  at  the  end  of 
the  course  traversed  by  the  impulses.  It  is  most  often 
placed  on  what  might  be  called  a  "spur-track,"  nearer  the 
central  than  the  peripheral  limit  of  the  neuron.  It  was 
long  a  question  whether  the  passing  impulses  entered  the 
perikaryon  or  left  it  quite  at  one  side  as  they  ran  inward. 
There  is  some  reason  to  think  that  they  actually  visit  it. 
By  a  rather  arbitrary  stretching  of  our  terms  we  may 
regard  the  section  of  such  a  neuron  that  lies  between  the 
periphery  and  the  perikaryon  as  an  elongated  dendrite, 
and  the  portion  central  to  the  perikaryon  as  the  axon. 
But  it  is  not  customary  to  call  a  fully  developed  and 
ensheathed  nerve-fiber  a  dendrite,  and  this  is  the  character 
of  the  conductor  in  question. 

When  we  think  of  the  limits  of  neurons  in  an  anatomic 
sense  it  is  well  for  us  always  to  have  their  physiologic 
action  in  mind.  If  we  do  so  we  can  speak  intelligibly  of 
beginnings  and  endings,  the  first  being  the  receptive 
processes,  and  the  second  the  terminals  which  transmit 
effects  to  other  neurons  or  to  tissues  not  belonging  to 
the  nervous  system  at  all.  The  afferent  or  receptor  neu- 
rons which  we  have  been  discussing  hegiyi,  in  this  sense, 
where  they  lie  exposed  to  stimulation  by  pressure,  heat 
or  cold,  or  chemical  agencies.  They  end  where  they 
form  synapses  with  other  neurons  in  the  gray  matter  of 
the  central  axis.  To  refer  to  beginnings  and  endings 
with  this  meaning  is  an  entirely  different  thing  from  using 
the  same  expressions  with  respect  to  origin  and  growth. 
We  cannot  deal  here  with  the  embryologic  facts. 


minutp:  structure  of  the  nervous  tissues    33 

The  neurons  belonging  in  the  class  of  adjustors  far 
outnumber  the  others  in  any  system  which  can  be  said 
to  be  highly  organized.  Such  neurons  are,  by  the  necessi- 
ties of  the  case,  intermediate  between  other  neurons. 
They  are  stimulated  through  their  dendrites  and  they 
are  assumed  to  discharge  through  their  axons.  A  single 
adjustor  neuron  may  have  a  long  axon  and  thus  span  a 
wide  space,  or  it  may  be  restricted  in  its  reach  to  a  micro- 
scopic scale.  When  the  processes  are  short  a  large  number 
of  neurons  in  series  may  be  concerned  in  carrying  im- 
pulses for  a  very  Hmited  distance.  Probably  this  kind  of 
transference  from  cell  to  cell  is  measurably  slower  than 
the  uninterrupted  flow  through  the  white  matter. 

Efferent  neurons  receive  through  their  dendrites 
stimuli  which  may  have  been  furnished  directly  from 
receptor  elements  or  which  may  have  arrived  by  way  of 
the  adjustors.  The  efferent  fibers  extend  usually  to  a 
considerable  distance  from  the  seat  of  their  origin  and 
terminate  by  making  connections  with  contractile  or 
secreting  cells.  When  mention  is  made  of  efferent 
fibers  one  is  most  apt  to  think  of  those  which  excite  the 
skeletal  muscles — motor  fibers  as  commonly  understood. 
Neurons  serving  this  purpose  run  an  unbroken  course 
from  cells  in  the  lower  part  of  the  brain  to  muscles  in  the 
head  and  neck;  others  similarly  pass  from  the  spinal  cord 
directly  to  muscles  in  the  trunk  and  limbs.  Efferent 
fibers  of  other  classes  are  usually,  if  not  always,  arranged 
in  tandem  fashion,  with  a  synapse  in  their  course,  so  that 
two  orders  have  to  be  traversed  by  impulses  bound  from 
the  brain  or  cord  to  many  peripheral  structures. 

We  have  pictured  the  nervous  elements  in  the  way 
which  has  been  considered  acceptable  until  quite  recently. 
But,  as  we  have  already  hinted,  the  neuron  theory  is 
under  a  fire  of  criticism.  We  must  take  pains  to  suggest 
possible  departures  from  the  doctrine  which  may  come 
to  be  estabhshed  in  time.  It  has  been  said  before  that 
continuity  of  protoplasm  from  neuron  to  neuron  is 
assumed  by  many.    The  view  that  a  synapse  is  a  bridge 

3 


34      THE   NERVOUS   SYSTEM    AND    ITS   COXSKKVATIUN 

rather  than  a  place  of  contact  impairs  the  .supposed 
individuaUty  of  the  units.  A  more  important  change 
in  our  conceptions  may  have  to  be  adopted  if  the  observa- 
tions of  certain  students  are  confirmed. 

The  statement  that  the  axon  of  a  nerve-fiber  may 
contain  a  numl^er  of  fibrils,  perhaps  to  be  regarded  as 
independent  carriers  of  impulses,  will  be  recalled.  It 
is  claimed  that  in  some  cases  fibrils  like  these  are  to  be 
demonstrated  within  the  perikarya  and  extending  out 
into  the  dendrites.  The  suggestion  has,  therefore,  been 
made  that  everj^thing  else  in  the  nervous  sj^stem  is  sub- 
ordinate in  importance  to  a  continuous  network,  slender 


Fig.  7. — To  illustrate  the  conception  of  the  neuropile  which 
subordinates  the  cells  of  the  nervous  system  to  a  continuous  net- 
work of  fibrils  sometimes  within  and  sometimes  without  the  cell 
boundaries. 

and  intricate.  This  it  is  proposed  to  call  the  neuropile. 
A  synapse,  in  the  light  of  this  interpretation,  is  merely 
the  place  where  fibrils  pass  from  the  sphere  of  influence 
of  one  perikaryon  to  that  of  another  (Fig.  7). 

The  chief  result  of  these  recent  discoveries  will  probabty 
be  to  lessen  the  prominence  given  to  the  perikarj^a  in 
descriptions  of  nervous  activity  and  to  emphasize  the  part 
played  by  the  fibrillar  conductors.  One  interesting  func- 
tion of  the  perikarya  remains  undisputed.  This  is  the 
responsibility  for  the  maintenance  of  normal  nutrition 
through  all  the  processes  of  the  neuron.  No  matter  how 
far  an  axon  may  stretch  from  the  cell-body  to  which  it 


MINUTE    STRUCTURE    OF   THE    NERVOUS  TISSUES      35 

belongs,  its  most  distant  portion  is  yet  dependent  upon 
the  influence  of  the  perikaryon  for  its  preservation  in  good 
condition.  Cut  off  from  its  perikaryon  it  inevitably 
degenerates.  This  is  a  fact  which  has  proved  most  help- 
ful to  the  investigators  who  have  sought  to  unravel  the 
tangled  fabric  of  the  nervous  system. 

Regeneration. — When  a  nerve  has  been  cut  and  de- 
generation has  taken  place,  regeneration  remains  a  possi- 
bility. This  requires  months  for  its  accomplishment. 
New  axons  from  the  old  perikarya  grow  along  the  track 
of  the  former  set.  It  seems  marvellous  that  they  should 
push  through  to  make  appropriate  connections,  but  they 
often  do.  Of  course,  this  may  be  prevented  by  obstacles 
in  the  path;  if  the  two  ends  of  the  cut  nerve  were  dis- 
placed laterally  instead  of  remaining  in  end-to-end  con- 
tact the  outgrowth  of  the  fresh  fibers  would  not  occur. 
Unfortunately  for  the  human  race,  the  reconstruction  of 
nerve-fibers  which  we  observe  outside  the  cord  and  brain 
does  not  take  place  in  the  central  axis.  Injuries  which 
result  in  degeneration  within  the  confines  of  the  central 
nervous  system  are  anatomically  irreparable.  Physio- 
logically, the  accompanying  losses  are  sometimes  made 
good  by  the  substitution  of  other  paths  for  those  which 
have  suffered  interruption. 


CHAPTER  III 
THE  ELEMENTS   OF  NERVE  PHYSIOLOGY 

It  was  impossible  to  discuss  the  structure  of  the  iKjrvous 
tissues  without  anticipating  to  some  extent  an  exposition 
of  their  working.  We  can  now  proceed  further  with  this 
subject.  We  have  chosen  the  word  "coordination"  to 
express  the  broad  function  of  the  system,  and  we  have 
said  that  the  chief  property  of  its  elements  is  conductivity. 
The  simplest  statement  of  the  duty  discharged  has  been 
said  to  be  something  like  this:  The  receptors  lie  exposed 
to  external  stimulation,  thence  the  effects  of  this  stimula- 
tion are  conveyed  to  the  adjustors  in  the  central  axis, 
the  adjustors  distribute  to  efferent  neurons,  and  by  these 
the  responses  of  muscles  and  glands  are  secured.  It  is  now 
time  to  inquire  into  the  nature  of  the  external  stimuli  and 
the  transmitted  energy. 

Stimuli. — A  stimulus  is  a  change,  physical  or  chemical, 
which  is  capable  of  producing  physiologic  reactions.  Rais- 
ing the  temperature  of  a  selected  area  of  the  skin  is  a 
means  of  stimulation.  Lowering  the  temperature  may 
have  equally  positive  results.  The  application  of  press- 
ure at  any  spot  whence  it  may  be  conducted  to  underly- 
ing receptors  is  an  instance  of  mechanical  stimulation. 
There  are  in  the  surface  of  the  tongue  receptors  which 
can  be  excited  by  various  dissolved  substances.  Here 
we  have  an  example  of  chemical  stimulation.  When  the 
retina  is  acted  on  by  hght  and  impulses  flow  along  the 
optic  nerve  to  the  brain  there  are  probably  two  steps  in 
the  process:  first,  the  light  causes  a  chemical  change,  as 
it  docs  in  the  photographic  plate;  second,  some  product 

36 


THE    ELEMENTS   OF    NERVE   I'HYSIOLOGY  37 

of  the  reaction  behaves  as  a  chemical  stimulant.  Electric 
currents — or,  more  correctly,  changes  in  electric  condi- 
tion— are  among  the  most  valuable  forms  of  stimuli 
for  experimental  purposes,  though  they  do  not  play 
any  considerable  part  in  the  natural  course  of  events. 

The  power  of  a  stimulus  to  ehcit  responses  depends 
upon  the  magnitude  of  the  change  from  previous  condi- 
tions. This  might  be  confidently  predicted,  but  another 
equally  important  fact  might  easily  be  overlooked. 
Stimuli  are  effective  not  only  in  proportion  to  their  am- 
plitude, but  also  in  proportion  to  the  rate  at  which  the 
change  takes  place.  In  other  words,  changes  sufficiently 
gradual  may  fail  of  stimulating  effect  even  though  they 
are  most  extensive.  Demonstration  of  this  is  secured  most 
conveniently  when  the  stimuli  observed  are  electric;  it  is 
found  that  rapid  shifting  of  potential  is  far  more  exciting 
than  a  slower  change,  while  the  alteration  may  be  made 
so  gradual  as  to  lose  all  efficacy. 

One  more  fact  concerning  stimuli  deserves  emphasis  at 
this  point.  The  withdrawal  of  an  influence  which  has 
been  operating  upon  the  hving  mechanism  may  be  as 
truly  a  stimulus  as  would  the  application  of  a  new  form 
of  energy.  Cold,  which  is  to  the  physicist  a  negation, 
must  be  counted  a  positive  means  of  physiologic  stimu- 
lation. The  same  may  be  said  of  sudden  darkness  or 
silence.  When  the  baby  has  gone  to  sleep  the  parent 
must  not  break  off  his  lullaby  too  abruptly.  He  should 
rather  employ  a  judicious  diminuendo,  when,  if  successful, 
he  will  have  illustrated  more  than  one  biologic  law.  At 
sea  we  wake  from  sleep  when  the  regular  throb  of  the  en- 
gine ceases. 

In  the  early  speculations  of  philosphers  respecting  the 
manner  of  action  of  nerves  the  picture  frequently  pre- 
sented is  that  of  tubular  conduits  giving  direction  to 
spurts  or  pulses  of  fluid.  One  is  reminded  of  the  pneu- 
matic appliances  sometimes  used  in  church  organs  to 
transmit  the  effect  of  pressure  upon  a  key  to  a  distant 
valve.     All  such  comparisons  are  wholly  faulty  and  we 


38      THE    NERVOUS    SYSTEM   AND   ITS    CONSERVATION 

must  utterly  discard  thcni.  The  nerves  are  not  tubes, 
but  cables,  and  even  the  axons  give  no  evidence  of  any 
progressive  movement  of  their  substance.  We  have  to 
do  with  conductors  in  which  the  material  is  stationary; 
this  is  an  important  limitation  as  we  strive  to  conceive  of 
the  propagated  impulse. 

If  we  think  of  instances  of  conduction  outside  the 
nervous  system  we  shall  be  attracted  by  the  figure  of  a 
fuse.  The  spark  which  runs  along  the  train  of  powder  is 
the  visible  sign  of  a  destructive  chemical  change.  A 
protoplasmic  strand  might  be  imagined  through  which  a 
similar  chemical  change  should  make  its  way,  leaving 
behind  it  a  track  barren  of  further  possibilities  in  the  line 
of  conduction.  Of  course,  this  does  not  correspond  closely 
with  what  we  know  to  be  true  of  the  nerves;  they  are 
adapted  to  carry  impulse  after  impulse  without  showing 
impairment.  The  extreme  resistance  of  white  matter  to 
fatigue  has  made  it  hard  to  believe  that  its  axis-cylinders 
are  in  any  sense  "burnt  out"  in  the  performance  of  their 
function.  We  cannot  think  that  there  is  any  extensive 
waste  of  material  as  the  unseen  impulses  travel  along 
the  paths  laid  for  them. 

Conductors  of  physical  changes  are  not  necessarily 
altered  in  the  least  by  their  service.  An  iron  wire  is  not 
worn  out  by  the  passage  through  it  of  the  electric  current. 
It  has  not  contributed  energy  from  its  own  stores,  as  has 
the  fuse,  to  reinforce  that  which  ran  from  one  end  of  it  to 
the  other.  All  the  energy  has  come  from  outside  the 
conductor,  and  when  that  energy  is  gone  the  wire  is  left 
sensibly  unaffected.  In  the  same  way  the  harp-string, 
which  is  plucked  near  one  end  and  is  swept  throughout 
its  length  by  the  resulting  vibrations,  comes  to  rest  un- 
changed except  for  a  trifling  wear  and  tear.  Here  again 
the  energy  came. from  outside  and  the  conductor  gave  up 
none  of  its  own.  The  nerve-fiber  seems  much  more 
like  the  wire  that  carries  the  current  or  the  musical  string 
set  in  vibration  than  like  the  fuse  consumed  in  doing  its 
duty.     Yet  we  must  not  hastily  conclude  that  a  nerve- 


THE    ELEMENTS    OF    NERVE    PHYSIOLOGY  39 

impulse  is  an  electric  current,  nor  that  it  can  be  called  a 
vibratory  disturbance.  We  must  not  hastily  abandon  the 
idea  that  it  has  chemical  features. 

A  chemical  change  occurring  in  white  matter  need  not 
be  destructive  in  character.  It  may  take  place  in  one 
instant  and  be  reversed  in  the  next  with  the  restoration 
of  the  initial  condition.  Something  like  this  must  be 
true  of  the  retinal  cells  in  which  the  Ught-waves  are 
momentarily  causing  photochemical  reactions  which  are 
almost,  though  not  perfectly,  neutralized  by  the  recupera- 
tive changes  which  accompany  them.  It  may  be  that  when 
'a  nerve-impulse  passes  there  is  a  disruption  of  molecules 
and  an  almost  instantaneous  recovery.  It  has  been  sug- 
gested that  upon  the  passage  of  each  impulse  a  sHght 
contribution  is  made  to  the  axon  by  the  enclosing  sheaths 
and  that  in  this  way  the  conductivity  is  maintained  almost 
indefinitely.  If  there  is  any  consumption  of  substance 
attendant  on  the  transfer,  we  should  expect  to  obtain 
evidence  of  the  formation  of  waste-products  in  nerve- 
trunks  which  have  been  functioning  for  a  long  time.  The 
fact  that  no  conclusive  evidence  of  this  sort  has  been 
secured  shows  that  the  conduction  process  is  one  of  extra- 
ordinary economy  of  material.^ 

One  is  constantly  tempted  to  present  the  plan  and 
working  of  the  nervous  system  in  terms  of  an  electric 
plant  like  that  of  a  telephone  exchange.  Nothing  made 
by  man  is  so  hke  the  nervous  mechanism,  with  its  channels 
leading  in  and  out,  and  shifting  connections  to  mediate 
between  them.  Moreover,  as  we  have  hinted,  there  is  an 
electric  change — slight,  but-  definite  and  characteristic — 
which  betrays  the  passage  of  each  nervous  impulse.  The 
flying  energy  is,  nevertheless,  not  to  be  regarded  as  an 


'  Even  while  these  statements  stand  in  manuscript  comes  the 
statement  of  the  Japanese,  Tashiro,  that  he  has  demonstrated  an 
augmented  discharge  of  carbon  dioxid  from  a  nerve-trunk  convey- 
ing impulses.  His  method  is  one  of  remarkable  delicacy  (American 
Journal  of  Physiology,  Proceedings  of  the  American  Physiological 
Society,  1913,  xxxi,  22). 


40      TH1-:    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

ordinary  electric  current.'  It  lias  no  such  inconceivable 
velocity.  About  the  middle  of  the  last  century  Hehn- 
holtz  reported  that  he  had  measured  the  rate  at  which 
the  impulses  pass  in  the  nerves  of  frogs  and  that  he  had 
found  it  to  be  less  than  100  feet  per  second.  Recent 
studies  have  made  it  probable  that  it  is  considerably 
higher  in  man,  ]>ut  it  is  not  by  any  means  equal  to  the 
speed  of  sound-waves  in  the  air. 

A  most  important  question,  and  one  which  is  proving 
difficult  to  answer,  relates  to  the  part  played  by  the  peri- 
karya  when  impulses  are  passing.  Do  these  spend  their 
own  substance  to  reinforce  the  transmission?  If  they  do 
they  are  like  the  relay  cells  in  telegraphic  sj'^stems.  Wires 
are  not  worn  out  with  carrjdng  electric  currents,  but 
batteries  are  used  up  in  generating  them.  It  has  been 
the  common  belief  that  the  perikarya  of  the  gray  matter 
do  suffer  disintegration  when  the  neurons  to  which  they 
belong  are  active.  It  is  usual  to  say  that  when  a  neuron 
is  stimulated  through  its  dendrites  there  is  a  discharge, 
meaning  by  this  an  evolution  of  fresh  energy  at  the  cost 
of  material  oxidized  or  otherwise  degraded.  Assuming 
this  to  be  true,  we  shall  have  an  outflow  of  energj^  greater 
than  that  applied  as  a  stimulus. 

We  could,  perhaps,  miagine  a  nervous  organization 
such  that  no  energy  save  that  originally  applied  by  the 
external  stimulus  should  be  observed  to  flow  from  it. 
This  would  be  economic  to  the  last  degree.  But  it  seems 
unlikety  that  anj^  tissue  can  ever  become  so  specialized 
as  to  lose  all  trace  of  its  primitive  tendency'  to  undergo 
some  decomposition  as  a  necessary  part  of  its  activity. 
When  contractile  elements  are  stimulated  they  respond 

1  Two  investigators,  Crehore  and  ^^'il]iams,  of  New  York,  have 
recently  attracted  much  notice  by  their  contention  that  nerve- 
impulses  are  actually  electric  in  their  nature.  By  taking  into  account 
the  dimensions  of  the  fibers  and  assigning  certain  physical  proper- 
ties to  the  sheaths  they  put  forth  an  argument  to  prove  that  electric 
disturbances  should  not  jiuss  very  rapidly  in  nerves,  but  rather  at 
about  the  velocity  found  to  hold  for  the  nerve-impulses.  It  is  too 
soon  to  say  whether  ph3siologists  will  generally  be  won  to  this  con- 
ception. 


THE    ELEMENTS   OF   NERVE    PHYSIOLOGY  41 

by  a  display  of  energy  utterly  out  of  proportion  to  that 
which  was  brought  to  bear  to  excite  them.  We  say  that 
the  force  they  exert  had  its  source  in  the  chemical  changes 
that  took  place  in  their  protoplasm,  changes  that  must 
have  left  the  tissue  in  an  altered  condition  and  with  a 
lessened  potency  for  further  performance. 

A  mechanical  analogy  suggests  itself.  Consider  the 
operation  of  the  lock  of  a  gun.  The  trigger  is  pulled  and 
the  hammer  falls,  but  not  with  the  slight  force  applied 
to  the  trigger.  It  comes  down  with  the  power  represented 
by  the  previous  tension  of  the  strong  coiled  spring.  The 
"stimulus"  released  an  internal  store  of  energy.  This  is 
representative  of  the  conditions  exhibited  by  muscles, 
and  it  is  probable  that  with  the  neurons  there  is  only  a 
difference  in  degree,  not  in  kind.  When  we  think  of  the 
trifling  amount  of  those  forces  which  often  prove  suffi- 
cient to  produce  extensive  reactions  of  the  organism  we 
can  hardly  doubt  that  the  currents  which  are  started 
from  the  receptors  receive  a  very  marked  reinforcement  at 
the  cost  of  the  gray  matter. 

We  have  some  definite  evidence  bearing  upon  this 
point.  If  the  perikarya  make  contributions  from  their 
own  stores  to  forward  the  nerve-impulses  we  may  expect 
them  to  show  fatigue  and  structural  change  in  connec- 
tion with  long-sustained  action.  Changes  associated  with 
activity  have  been  frequently  described.  Some  years  ago 
Hodge  announced  that  there  is  a  clear  difference  between 
the  outline  and  internal  appearance  of  the  perikarya  in  the 
gray  matter  of  animals  killed  after  a  night's  sleep  and  the 
corresponding  features  as  seen  in  specimens  from  animals 
killed  at  the  close  of  the  day.  He  obtained  his  material 
from  birds  whose  intense  life-processes  might  be  expected 
to  make  them  most  favorable  subjects.  The  statements 
of  Hodge  have  been  widely  confirmed.  We  must  discuss 
this  important  matter  again  in  connection  with  the  topic 
of  fatigue. 

We  shall  assume  provisionally  that  nerve-impulses  may 
be  set  going  in  the  conducting  pathways  either  by  the 


4,2      THE   NERVOUS    SYSTEM    AND    ITS   CONSERVATION 

direct  effect  of  external  stimuli  or  by  the  chemical  changes 
occurring  in  the  perikarya.  The  impulses  that  run  along 
the  afferent  (receptive)  channels  are  originated  in  a 
relatively  direct  manner  by  external  forces.  Those  that 
traverse  the  adjustors  and  run  out  to  the  effectors  may  be 
thought  of  as  the  afferent  currents  which  have  continued 
through  the  synapses  of  the  central  axis,  but  we  shall 
probably  do  well  to  regard  them  rather  as  relays,  that  is, 
impulses  started  anew  from  perikarya  excited  to  "dis- 
charge." This  view,  according  to  which  the  energy  of  the 
transmission  is  reinforced  by  each  neuron  in  the  series, 
is  the  older  doctrine  and  is  still  dominant. 

Attention  must  now  be  called  to  the  relative  ease  with 
which  neurons  will  respond  to  stimuK  applied  at  different 
points.  It  is  most  necessary  for  the  orderly  and  purposeful 
working  of  the  nervous  system  that  nerve-fibers  shall  not 
be  easily  excited  save  at  their  specialized  beginnings  or 
endings.  It  is,  in  fact,  difficult  to  stimulate  a  nerve  at 
any  intermediate  point  in  its  course.  When  we  do  use 
sufficiently  positive  means  to  make  the  stimulation 
effective  the  result  is  such  as  to  remind  us  that  it  would 
be  undesirable  to  have  it  a  common  incident.  A  blow 
on  the  cl])ow  may  be  forcible  enough  to  start  impulses 
in  the  afferent  fibers  of  the  nerve  which  lies  near  the 
surface  at  that  spot,  and  it  instantly  seems  to  the 
subject  that  he  has  sensations  pertaining  to  the  wrist  and 
fingers.  He  has  excited  to  activity  the  axons  which  have 
habitually  brought  impulses  from  the  hand,  and  they  still 
awaken  the  same  associations  as  though  they  had  come 
over  the  whole  distance.  This  is  a  very  significant 
matter  and  it  will  be  wise  to  place  further  emphasis 
upon  it. 

When  an  electric  door-bell  rings,  the  householder  is 
usually  justified  in  the  assumption  that  some  one  is  out- 
side ringing  it.  Yet  it  might  happen  that  a  short-circuit 
at  some  point  along  the  course  of  the  wires  should  cause 
the  signal.  The  ringing  of  the  bell  when  occasioned  in 
this  abnormal  way  would  have  the  same  quahties  to  the 


THE    ELEMENTS    OF    NERVE    PHYSIOLOGY  43 

ear  that  had  previously  become  famiUar.  So  it  is  with  our 
sensations;  we  rely  on  the  regularity  of  their  external 
causation,  but  we  are  always  liable  to  be  misled  by  an 
experience  like  that  of  the  tingle  that  follows  the  rap  on 
the  elbow.  Impulses  started  anywhere  between  the 
periphery  and  the  central  stations  have  the  same  conse- 
quences for  us  as  though  they  had  been  initiated  at  the 
remotest  terminal  structures.  The  more  one  reflects  on 
this  fact,  the  more  one  marvels  at  the  freedom  from  con- 
fusing hallucinations  which  we  usually  enjoy. 

Are  nerve-impulses  all  alike?  This  is  a  most  interesting 
question.  The  first  disposition  will  be  for  one  to  say  that 
they  must  vary  widely  in  nature  to  produce  such  dis- 
similar effects.  But  most  of  our  physiologic  progress  has 
been  found  consistent  with  the  idea  that  they  vary  chiefly 
in  intensity  and  frequency  and  not  in  the  more  subtle 
ways  which  might  be  conceived.  The  reader  must  be 
reminded  that  two  electric  currents  precisely  alike  in 
themselves  may  cause  utterly  unlike  phenomena  if  they 
are  led  through  different  fixtures.  The  closing  of  one 
circuit,  for  example,  may  ring  a  bell;  the  closing  of  another 
may  light  a  gas-jet.  It  is,  for  the  most  part,  quite  as 
unnecessary  to  suppose  that  different  nerves  carry  im- 
pulses of  contrasted  character  as  to  assume  that  the 
electric  currents  are  mysteriously  differentiated  in  the 
case  cited.  The  clarifying  view  that  they  are  essentially 
similar  throughout  the  whole  system  is  one  which  we  owe 
primarily  to  the  great  physiologist,  Johannes  Miiller 
(1801-1858).  The  theory  encounters  many  difficulties, 
but  is  not  to  be  prematurely  abandoned. 

Teaching  experience  shows  that  students  find  it  ex- 
ceedingly hard  to  beheve  that  the  impulses  passing  along 
various  nerve-trunks  are  of  one  unvarying  character.  The 
instructor  is  at  great  pains  to  dissuade  them  from  speaking 
of  "messages"  or  "sensations"  in  this  connection.  Mes- 
sages and  sensations  are  evolved  from  nerve-impulses 
only  by  a  process  of  translation;  these  highly  colored 
words  cannot  properly  be  applied  to  the  energy  in  transit. 


44      THE    NKUVOIS    SYSTEM    AND    ITS   COXSKHVATIOX 

Psychologists  have  entertained  and  disciplim-d  their  i)u- 
pils  by  sup;j2;csting  what  would  be  the  result  of  diverting 
the  impulses  from  one  sense  organ  so  that  they  should 
enter  the  brain  over  a  route  normally  belonging  to  a  differ- 
ent receptor  system.  The  favorite  proposition  is  to  demand 
that  impulses  originating  in  the  eye  be  switched  to  the 
auditory  path,  and  that  those  generated  in  the  ear  be 
led  into  the  brain  along  the  fibers  of  the  optic  nerve. 
The  subject  must  then  hear  all  that  he  used  to  see  and 
see  all  that  he  formerly  heard.  The  lightning  will  be 
for  him  a  short,  sharp  sound,  and  the  thunder  a  pro- 
longed, flickering  light.  At  a  concert  he  will  hear  the 
lights,  the  decorations,  and  the  costumes,  but  he  will 
have  the  extraordinary  privilege  of  seeing  the  progres- 
sions of  the  music.  We  cannot  anticipate  at  all  how  it 
will  look. 

Unprofitable  as  such  flights  may  appear,  they  at  least 
afford  a  clear  recognition  of  the  "Miillerian  principle." 
According  to  this  the  diverse  effects  produced  by  nerve- 
impulses  in  various  cases  are  due  entirely  to  the  direc- 
tion which  these  impulses  are  made  to  take  within  the 
nervous  system,  and  not  at  all  to  their  own  variability. 
Moreover,  the  effects  of  stimulation  must  be  determined 
far  more  by  the  choice  of  fibers  to  be  acted  upon  than  b}'' 
the  kind  of  stimulation  employed.  The  optic  fibers  are 
usually  made  to  bear  impulses  which  have  been  initiated 
in  the  retina  under  the  influence  of  light,  but  it  is  possible 
to  start  impulses  along  these  same  fibers  by  other  means. 
Thus,  it  is  recalled  from  the  old  days  of  surgery  without 
anesthetics  that  the  cutting  of  the  optic  nerve — a  form 
of  mechanical  stimulation — was  not  productive  of  pain 
beyond  that  alread}''  being  endured,  but  of  the  sensation 
of  a  flash  of  light.  It  is  not  certain  that  we  can  always 
adhere  strictly  to  the  doctrine  of  the  uniform  character 
of  the  nerve-impulses,  but  to  do  so  as  far  as  possible  makes 
for  clearness. 

It  is  well  just  here  to  refer  to  a  phenomenon  often  held 
to  be  mysterious,  though  readily  explained.     This  is  the 


THE   ELEMENTS    OF    NERVE    PHYSIOLOGY  45 

persistence,  after  amputation,  of  sensations  long  associated 
with  the  member  that  has  now  been  lost.  The  experience 
is  said  to  be  vivid  and  distressing.  Spiritualistic  theories 
have  been  advanced  with  regard  to  it.  But,  after  all,  it 
is  just  what  we  ought  to  expect.  The  stump  contains 
all  the  fibers  that  were  formerly  concerned  in  bringing 
the  impulses  from  the  missing  limb.  If  certain  ones 
are  subjected  to  unusual  tension  or  pressure  in  the  read- 
justment of  the  tissues  attendant  upon  the  heaUng  process, 
impulses  may  be  started  along  the  old  channels.  All  the 
associations  of  the  resulting  sensations  will  be  with  the 
peripheral  localities  from  which  impulses  used  to  arrive 
over  these  routes. 

Summary. — We  are  now  in  a  position  to  sum  up  the 
substance  of  the  last  few  pages.  The  white  matter  of  the 
nervous  system  serves  to  conduct  impulses — which  can 
usually  be  considered  quite  lacking  in  individuality — 
to  and  from  places  in  the  gray  matter.  The  paths  in  the 
white  matter  are  permanent.  For  the  most  part,  at  least, 
they  exist  from  infancy  and  are  changed  only  by  gross 
pathologic  processes.  Conductivity,  the  course  a  fixed 
one,  is  the  distinctive  property  of  the  fibers  as  it  is  of 
electric  wires.  If  this  is  true,  what  shall  we  say  of  the 
gray  matter?  We  shall  be  inclined  to  credit  it  with  the 
power  of  reinforcement,  as  already  pointed  out,  but 
here  too  we  must  continue  to  emphasize  the  duty  of  con- 
ducting. A  most  important  difference  between  the  con- 
trasted kinds  of  nervous  tissue  is  found  in  the  varying 
direction  taken  by  impulses  traversing  the  gray  matter 
at  different  times  as  compared  with  the  inflexible  be- 
havior of  the  white.  If  we  liken  the  nerve-fibers  to  wires, 
as  we  have  just  done,  we  may  find  in  a  switch-board  a 
partial  analogy  to  the  gray  matter.  Wires  and  switch- 
boards both  serve  to  conduct  currents,  but  the  latter 
permit  the  interruption  and  the  resumption  of  the  con- 
duction and  the  most  extensive  shifting  of  connections 
between  channels  of  entrance  and  exit.  Similarly,  wc 
are  brought  to  recognize  that  an  inflowing  stream  of  im- 


46      THE    NERVOUS  SYSTEM    AND    ITS    CONSERVATION 

pulses  of  a  certain  intensity  may  under  soni,e  circumstances 
be  blocked  in  the  gray  matter,  while  under  other  condi- 
tions it  may  emerge  to  reach  the  effectors  more  or  less 
strikingly.  This  property  of  the  gray  matter  is  spoken  of 
as  variable  resistance.  Often  it  is  denominated  synaptic 
resistance,  on  the  basis  of  the  assumption  that  it  is  the 
synapses  as  previously  defined  which  so  greatly  change 
their  conductivitj^  from  time  to  time. 

A  little  reflection  will  convince  one  that  resistance  to 
the  passage  of  impulses  through  the  graj^  matter  must 
have  everything  to  do  with  the  behavior  of  the  organism. 
If  it  is  temporarily  lowered  to  a  certain  extent,  reactions 
will  be  readily  produced  by  stimuli  of  slight  intensity. 
If  it  is  lowered  still  further,  the  responses  will  become 
exaggerated,  confused,  and  exhausting.  Increase  of  re- 
sistance, on  the  other  hand,  will  render  it  more  and  more 
difficult  to  evoke  reactions.  Life  itself  has  been  defined 
approximately  as  a  continued  "adjustment  of  internal 
to  external  relations,"  and  the  biologic  term,  "irritabihty," 
stands  for  the  capacitj^  to  make  such  adjustments.  Evi- 
dently the  resistance  of  the  central  nervous  system  must 
be  maintained  between  limits  not  too  widely  separated  if 
the  good  of  the  organism  is  to  be  served. 

Not  only  does  the  resistance  of  the  central  gray  matter 
vary  under  the  influence  of  drugs  and  of  the  drug-hke 
products  of  the  body's  own  activity,  but,  what  is  of  yet 
greater  interest,  it  is  modified  by  the  prolonged  use  of  the 
structure  in  cpestion.  In  general,  repeated  reactions  are 
secured  with  more  and  more  ease.  This  is  a  fact  of  the 
utmost  import;  it  will  be  foreseen  that  it  must  be  the 
starting-point  for  any  discussion  of  habit  formation  and 
even  of  education.  We  say  that  paths  of  easy  transmis- 
sion tend  to  become  established  in  the  nervous  system  in 
connection  with  its  employment  in  a  routine.  These 
paths  are  the  "ruts"  of  everyday  speech.  The  evidence 
that  they  come  to  exist  is  found  in  physiology  rather  than 
anatomy,  that  is,  in  observed  behavior  rather  than  in 
visible  structural  features  of  the  gray  matter,   but  we 


THE    ELEMENTS    OF    NERVE    PHYSIOLOGY  47 

cannot  doubt  that  there  are  actual  material  changes 
in  the  tissue,  though  it  is  not  Hkely  that  the  most 
refined  microscopic  technic  will  ever  make  them  recog- 
nizable. 

It  will  now  be  apparent  that  while  conductivity  is  the 
most  conspicuous  property  of  all  nervous  systems,  it  has 
associated  with  it,  though  in  a  varying  degree,  the  capacity 
to  be  modified  by  use.  The  power  to  conduct  impulses 
along  fixed  pathways  with  fixed  reactions  ensuing  is  highly 
characteristic  of  those  forms  of  life  which  we  regard  as 
lower  and  simpler.  The  second  power  is  obviously  pro- 
portional to  the  rank  which  we  involuntarily  assign  to 
animals.  So  far  as  they  possess  it,  they  have  the  chance 
to  profit  by  individual  experience.  This  would  seem  to  be 
the  same  thing  as  inteUigence  objectively  viewed.  Com- 
plexity of  action  does  not  necessarily  imply  such  an 
endowment.  We  marvel  at  the  community  life  of  bees, 
and  we  are  inclined  to  endorse  Darwin's  assertion  that 
the  brain  of  the  ant  is  the  most  wonderful  particle  of 
matter  in  the  universe,  but  upon  reflection  we  are  led  to 
give  cats  and  dogs  credit  for  immeasurably  superior 
organization. 

An  old  ant  is  probably  Kttle  better  than  a  young  one 
in  meeting  the  exigencies  of  its  environment.  Maturity 
in  the  insect  is  a  matter  of  size  and  strength  rather  than 
any  acquirement  of  profitable  responses  to  stimulation. 
But  maturity  in  the  dog  means  an  acquirement  of  just 
such  responses  and  it  also  means  that  dogs  have  indi- 
viduality. The  inherited  nervous  mechanism  in  the  one 
case  is  all  but  rigid;  in  the  other  it  is  plastic  in  a  high  de- 
gree. We  cannot  deny  to  the  ant  some  trace  of  this 
capacity  for  modification  through  experience;  the  ability 
to  return  to  the  nest  seems  to  dentonstrate  it,  but  we  do 
not  expect  to  find  it  impressive.  It  will  be  noted  that  the 
plastic  property  is  met  with  in  those  nervous  systems 
which  in  the  beginning  of  the  animal's  life  are  most 
inadequately  fitted  to  meet  the  demands  made  upon  them. 
We  might  conceive  of  a  nervous  system,  as  well  prepared 


48    THK  ni<:rvous  systp:m  axd  its  conservation 

to  make  the  necessary  adjustments  as  is  that  of  the  ant, 
which  should  nevertheless  record  the  unique  history  of 
the  sinfi;le  life,  but  such  a  combination  is  unknown.  Our 
chief  interest  is  in  the  human  beinf>;,  and  it  is  self-evi- 
dent that  the  nervous  system  of  man  is,  at  the  outset, 
the  farthest  from  being  ready  to  cope  with  the  environ- 
ment as  it  is  the  best  adapted  to  register  individual 
contacts. 


CHAPTER  IV 

REFLEXES 

We  have  said  repeatedly,  in  one  form  and  another, 
that  it  is  the  duty  of  the  nervous  system  to  produce 
timely  adjustments  to  changing  environmental  condi- 
tions. These  ■  adjustments  are  called  reflexes.  The 
statement  has  already  been  made  that  a  receptor  neuron 
Hnked  to  an  effector  is  the  simplest  possible  "reflex  arc." 
It  is  now  time  to  enlarge  upon  these  matters. 

The  word  ''reflex"  readily  suggests  the  word  "reflec- 
tion." The  elementary  conception  is  of  an  influence 
brought  to  bear  upon  the  central  nervous  system  from 
without  and  rebounding  to  contractile  or  glandular 
structures  which  are  aroused  to  activity.  This  is  a  de- 
cidedly crude  notion  and  must  be  dismissed  in  favor  of  a 
more  accurate  description.  Descartes,  in  the  seventeenth 
century,  attempted  to  account  for  the  familiar  reactions 
of  animals  to  stimuh  in  terms  like  the  following:  "Nerves 
are  made  up  of  fine  tubular  conductors  connected  with 
reservoirs  of  a  peculiar  fluid  in  the  brain.  These  tubes 
contain  slender  threads  which  are  attached  to  valves 
controlhng  the  outflow  of  this  fluid.  When  there  is  a 
disturbance  at  the  exposed  ends  of  some  of  these  con- 
ductors the  threads  are  pulled  and  the  valves  opened. 
Thereupon  the  energizing  fluid  runs  down  the  same  tubes 
and  enters  the  substance  of  the  muscles,  which  are  at 
once  thrown  into  contraction."^ 

This  is  not  a  correct  exposition  of  the  mechanism,  but  it 
is  a  creditable  effort.  It  can  be  paraphrased  in  such  a  way 
as  to  lose  much  of  its  fantastic  aspect.    We  can  recognize 

1  Foster,  "Lectures  on  the  History  of  Physiology,"  Cambridge 
University  Press,  1901,  chap.  x. 

4  49 


50      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

here  the  afferent  fibers  conveying  a  form  of  energy  from 
the  outljdng  region  to  the  central  organs,  the  resulting 
release  of  fresh  energy  there,  and  the  conveyance  of  the 
returning  impulses  to  the  contractile  tissues.  We  do  not 
now  believe  that  the  incoming  and  outgoing  energies 
differ  in  any  such  qualitative  fashion  as  Descartes  sup- 
posed, but  wc  can  recognize  in  his  description  the  impor- 
tant truth  that  the  efferent  flow  is  much  more  voluminous 
than  the  afferent.  If  we  consider  typical  cases  we  shall 
come  to  appreciate  the  striking  disproportion  between  the 
two. 


Fig.  8. — ^The  afferent  neuron  influences  directlj^  four  efferent  neu- 


rons. 


Take,  for  example,  the  wink  which  is  caused  by  the 
contact  of  a  minute  particle  with  the  surface  of  the  eye. 
The  area  stimulated  may  be  so  small  that  we  can  scarcely 
think  that  more  than  a  single  nerve-fiber  is  concerned 
in  the  afferent  transmission  which  follows.  Yet  to  pro- 
duce the  muscular  response  a  very  large  number  of  fibers 
must  be  made  to  bear  impulses  to  the  muscles  involved. 
Perhaps  the  coughing  reflex  will  serve  our  purpose  even 
better.  Here  an  irritating  particle  hardly  larger  than 
that  required  to  cause  the  wink  may  act  upon  the  central 


REFLEXES 


51 


nervous  system  from  the  larynx,  with  the  result  that 
most  of  the  conspicuous  trunk  muscles  are  made  to  share 
in  the  convulsive  response.  It  is  easy  to  account  for  this 
spread  of  the  impulses  in  the  hght  of  the  apparent  ana- 
tomic organization  of  the  gray  matter. 

The  general  rule  seems  to  be  that  one  afferent  neuron 
makes  connections  with  a  number  of  efferent  elements. 
A  diagram  (Fig.  8)  will  be  helpful.     It  is  possible  by  an 


Fig.  9. — The  adjustors  extend  the  effect  to  a  greater  number  of 
eifei-ent  paths. 


extension  of  this  principle  to  visualize  a  mechanism 
which  will  insure  the  most  multifarious  discharge  of  im- 
pulses after  a  solitary  afferent  conductor  has  been  ex- 
cited. But  the  painstaking  histologists  who  have  done 
most  to  interpret  the  finer  structure  of  the  gray  matter 
believe  that  the  spread  of  the  process  is  accomplished 
largely  through  the  interposition  of  neurons  of  a  third 
order  between  those  which  are  clearly  afferent  and  those 
which  are  definitely  efferent.     These,  according  to  our 


52     THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

preliminary  classification,  may  be  called  adjusters.  An- 
other diag;ram  (Fig.  9)  may  be  introduced  to  show  the 
relation  of  the  adjusters  to  the  reflex  act. 

There  is  an  evident  economy  in  this  arrangement.  It 
brings  large  clusters  of  efferent  neurons  under  the  control 
of  single  afferent  units.  ^Moreover,  there  is  no  doubt 
that  adjusters  such  as  we  have  pictured  are  often  domi- 
nated bj'  others  of  a  still  higher  order.  Thus  we  see  in  the 
nervous  system  an  organization  like  that  of  an  army,  in 
which  generals  are  placed  over  colonels,  colonels  over 
captains,  etc.  In  the  army  the  number  of  officers  holding 
a  given  rank  is  greater  than  the  number  of  their  superiors, 
but  less  than  the  number  of  their  subordinates.  In  the 
nervous  sj^stem  this  is  probably  true  of  the  units  in  many 
of  the  particular  mechanisms,  but  it  may  not  hold  in- 
variably, since,  quite  unlike  the  mihtarj'  condition,  a 
neuron  may  be  under  the  sway  of  a  number  of  others  of 
the  next  grade  above.  This  statement  introduces  the 
idea  that  now  one  and  now  another  element  may  be 
responsible  for  the  activit}^  of  the  same  inferior  group. 
It  also  suggests  that  there  may,  in  some  sense,  be  a  strife 
among  the  interlocking  neurons.  We  shall  have  future 
occasion  to  dwell  upon  the  conception  that  inhibitor}'  as 
well  as  excitaton^'  influences  may  be  exerted  by  certain 
neurons  upon  others. 

The  following  illustration  is  instructive:  A  man  had 
clunbed  out  of  a  sixth  story  window  which  he  was  to  clean. 
He  stood  wath  his  toes  upon  a  narrow  ledge,  holding 
meanwhile  to  the  upper  sash.  A  gust  of  wind  took  off  his 
hat  and  both  his  hands  went  instantly  to  his  head.  At 
once  his  bod}'  began  tilting  out  into  space.  His  hands 
fell  with  great  speed  and  force  upon  the  sash,  which, 
fortunately,  had  not  passed  out  of  reach.  Here  a  simple 
reflex,  normal  under  most  circumstances,  would  have 
proved  disastrous,  and  was  overruled  by  another  making 
for  self-pre.servation.  In  all  probability  no  reasoning 
process  preceded  the  .second  adjustment.  But  the  train 
of  reflections  that  followed  was  sufficiently  \'ivid,  and  the 


REFLEXES  53 

window-washer  crawled  back  into  the  room  and  lay  for 
a  while  upon  the  floor. 

As  we  are  constantly  speaking  of  nerve-centers,  it  is 
time  to  define  what  is  meant  by  that  expression.  A  center 
is  usually  assumed  to  be  a  collection  of  perikarya  mediat- 
ing a  definite  action  which  may  be  either  motor  or  secre- 
tory. The  center  is  a  station  to  which  impulses  flow  from 
different  sources  at  different  times,  but  which  transmits 
impulses  always  to  a  common  path.  When  mention  is 
made  of  a  center  one  thinks  naturally  of  a  circumscribed 
spot  in  the  nervous  system — an  anatomic  conception. 
But  it  is  necessary  to  bear  in  mind  at  the  same  time 
that  widely  separated  neurons  may  have  such  connec- 
tions that  they  will  be  unified  in  their  activities.  In 
other  words,  centers  may  have  a  physiologic  existence 
where  there  is  no  focal  assembling  of  the  cooperating 
units. 

When  we  try  to  draw  the  line  between  those  actions 
of  the  nervous  system  which  can  unhesitatingly  be  called 
reflexes  and  others  not  to  be  called  so,  we  fuid  ourselves  in 
the  midst  of  difficulties.  In  elementary  presentations  of 
the  subject  it  is  usual  to  distinguish  between  reflex  and 
"voluntary"  action,  but  the  more  we  observe  the  facts, 
the  less  satisfactory  this  attempted  distinction  appears. 
It  is  certainly  true  that  in  most  of  those  movements 
which  we  are  accustomed  to  call  voluntary  we  can  still 
recognize  the  directing  influence  of  external  conditions. 
This  is  a  way  of  saying  that  such  acts  partake  of  the 
reflex  character.  We  find  it  most  clearly  the  case  in 
monotonous  serial  movements  hke  those  of  walking.  We 
say  that  we  walk  because  we  will  to  do  so,  but  we  can 
hardly  claim  that  the  formation  of  a  conscious  purpose 
precedes  the  taking  of  each  step.  At  another  time  we 
may  analyze  more  fully  what  can  be  baldly  stated  here: 
that  each  position  assumed  by  the  body  and  Hmbs  of  the 
walker  establishes  stresses  within  and  contacts  without  of 
such  a  nature  as  to  dictate  the  appropriate  succeeding 
contraction. 


54      THE    NERVOUS   SYSTEM    A\D   ITS    CONSERVATION' 

In  the  human  subject  the  acts  which  arc  seen  to  be  car- 
ried out  by  the  newborn  are  alwaj's  classed  as  reflexes. 
Sucking,  coughino;,  sneezing,  hiccups,  vomiting,  crying, 
clutching,  drawing  up  of  the  legs,  and  other  examples 
will  occur  to  the  reader.  The  list  becomes  much  longer 
when  we  take  pains  to  include  some  which  are  not  so 
obvious  to  the  domestic  observer:  changes  in  the  size  of 
the  pupils,  changes  in  the  distribution  of  the  l^lood,  the 
discharge  of  sweat  and  other  secretions,  etc.  Swallowing 
is  essentiall}^  a  reflex  not  to  be  executed  unless  there  is  at 
least  a  little  moisture  to  be  removed  from  the  mouth. 

As  to  the  reactions  which  the  child  acquires  with  ad- 
vancing development,  we  find  no  satisfacory  standard 
which  will  enable  us  to  say  of  orie  that  it  is  a  reflex  and  of 
another  that  it  should  be  otherwise  named.  The  tendency 
is  to  restrict  the  term  "reflex"  to  those  responses  to 
external  stimuli  which  are  common  to  all  normal  indi- 
viduals, while  those  which  are  peculiar  to  certain  ones  we 
call  habits  or  mannerisms.  But  the  claim  may  be  stronglj^ 
defended  that  a  habit  is  a  personal  reflex — an  instance  of  a 
reaction  to  surrounding  conditions  given  more  or  less  of  an 
inevitable  character  by  the  acquired  structure  of  the 
subject's  nervous  system.  Nail-biting  may  be  regarded 
as  an  unfortunate  reflex  manifestation  in  which  the 
maltreated  finger-tips  are  sending  up  to  the  central 
axis  the  impulses  Avhich  dictate  further  attacks  upon 
them. 

When  we  pass  from  habits  to  accomplishments  we  must 
still  recognize  a  degree  of  connection  between  external 
stimuli  and  the  performance.  The  act  of  copying  a  word 
or  a  sketch  ma}^  transcend  the  reflex  as  commonly  under- 
stood, but  would  seem  to  include  its  distinctive  features. 
The  copy  set  is  a  source  of  visual  stimulation  and  the 
movements  of  the  pen  held  in  the  skilled  hand  are  -de- 
termined by  its  appearance.  Even  the  answering  of  a 
question,  it  may  be  asserted,  is  an  act  brought  to  pass  in 
consequence  of  the  penetration  of  auditory  impulses 
through  the  pathways  of  a  brain  prepared  to  react  to 


REFLEXES  55 

them.  But  we  shall  follow  the  usual  custom  and  restrict 
the  term  "reflex"  to  responses  the  capacity  for  which  is 
inborn  or  universally  acquired,  and  to  acts  which  occur 
as  surely  when  the  attention  is  occupied  with  other 
matters  as  when  they  are  themselves  under  scrutiny. 

Our  stock  illustrations  of  reflexes  are  apt  to  be  those 
in  which  brief  and  abrupt  movements  are  witnessed.  It 
is  well  to  remind  ourselves  that  adaptive  changes  of  this 
kind  may  be  gradual  and  sustained  in  character.  One  too 
easily  overlooks  the  more  continuous  services  of  the 
nervous  system.  Physiologists  apply  the  word  "tonic" 
to  such  actions  as  are  mild  in  degree,  but  maintained  over 
long  periods.  Under  normal  conditions  the  skeletal  mus- 
cles are  incompletely  relaxed;  we  say  that  the  nervous 
system  is  subjecting  them  to  a  tonic  stimulation.  This 
subdued  but  definite  activity  of  the  mechanism  is  the 
result  of  the  constant  inflow  of  impulses  from  various 
sources;  it  has  the  reflex  character.  The  slightly  con- 
tracted state  of  the  muscles  is  spoken  of  as  a  "reflex 
tonus."  We  speak  often  of  an  "arterial  tonus,"  a  sus- 
tained, moderate  contraction  of  the  small  blood-vessels 
for  which  a  particular  portion  of  the  nervous  system  is 
clearly  responsible.  We  may  not  be  warranted  in  saying 
that  this  tonic  condition  is  equally  with  the  other  of  a 
reflex  sort,  but  its  variations  are  so,  and  they  constitute 
an  interesting  chapter  in  physiology — that  which  deals 
with  the  vasomotor  reactions. 

"Conditioned  Reflexes." — Most  reflexes  seem  highly 
purposeful  in  the  sense  that  they  are  such  as  to  con- 
tribute to  the  well-being  of  the  animal.  In  certain  cases 
the  purposeful  character  cannot  be  recognized  and  the 
reflexes  appear  bizarre  and  illogical.  Some  hght  was 
cast  on  reactions  of  this  eccentric  sort  by  experiments 
reported  from  a  Russian  laboratory  a  few  years  ago. 
The  investigators  found  it  possible  to  j^oke  a  novel 
stimulus  with  one  which  was  familiar,  and  eventually  to 
confer  on  the  novel  stimulus  much  of  the  efficiency  which 
at  first  belonged  only  to  the  famihar  one.    The  following 


5b      THE    NHRVOUS    SYSTEM    AND    ITS    CONSERVATION 

is  a  simple  example:  A  dog  secretes  saliva  when  shown 
food  which  he  likes.  The  reaction  is  what  is  sometimes 
called  a  psycho-reflex.  The  trial  was  made  many  times, 
and  on  each  occasion  a  whistle  was  blown  while  the  food 
was  displayed.  At  len^h  the  blowing  of  the  whistle 
without  the  exhibition  of  the  food  sufficed  to  cause  sali- 
vation. 

The  acquired  capacity  of  the  nervous  system  to  excite 
the  salivary  glands  in  response  to  a  special  auditory 
stimulus  was  called  by  the  first  observer  a  "conditioned 
reflex."  Such  cases  afford  a  striking  proof  of  the  plas- 
ticit}'  of  the  adjustor  mechanism.  Yet  it  may  also  be  said 
that  thej^  afford  evidence  of  its  rigidity.  In  support  of 
this  last  statement  a  curious  fact  is  to  be  mentioned:  it 
was  found  that  when  a  dog  had  become  so  sensitized  that 
he  would  produce  saliva  when  the  whistle  was  blown,  his 
system  remained  quite  unresponsive  to  notes  a  very  little 
sharp  or  flat  as  compared  with  the  pitch  employed  in  the 
course  of  training.  It  is  reported  further  that  if  a  chord 
of  three  notes  was  used  instead  of  a  single  one  the 
sensitized  animal  would  secrete  saliva  on  the  produc- 
tion of  cither  of  the  simple  constituent  tones,  but  more 
for  two  sounded  together,  and  most  for  the  complete 
chord. 

Have  we  not  here  something  direct I3'  related  to  the 
mj'sterious  rajjport  of  hypnotism?  It  seems  strange  that 
a  human  subject  can  become  indifferent  to  all  voices 
save  one  and  yield  abject  obedience  to  that  controlling 
voice.  But  it  may  be  conceived  that  this  is  only  an 
elaborate  development  of  the  conditioned  reflex.  When 
the  hypnotic  state  was  induced  the  nervous  system  be- 
came attuned  to  the  particular  pitch  and  timbre  of  the 
speaker's  tones.  It  is  said  that  these  are  well  enough 
reproduced  by  the  phonograph  to  make  it  possible  to 
substitute  the  instrument  for  the  hypnotist. 

Probably  we  are  all  possessed  of  many  conditioned 
reflexes.  The  reactions  may  be  hard  to  detect  and  still 
harder  to  trace  to  their  sources  in  past  experience.    Never- 


REFLEXES  57 

theless,  frank  and  intelligent  people  can  often  furnish 
illustrations.  The  most  frequent  are  probably  connected 
with  the  large  intestine  and  the  bladder.  Certain  condi- 
tions which  have  no  logical  bearing  upon  the  functions  of 
these  organs  will  regularly  arouse  them  to  inconvenient 
activity.  A  friend  of  the  writer  cannot  mislay  an  article 
and  begin  to  search  for  it  without  having  an  immediate 
awakening  of  the  colon  to  energetic  movement.  On  some 
occasion  in  the  past  there  was  probably  a  coincidence  of 
the  two  circumstances  and  a  cross-tie  between  two 
mechanisms  has  remained.  Such  a  tie  has  undoubtedly 
an  anatomic  existence,  though  we  do  not  expect  to  have  it 
pointed  out  postmortem  in  the  mazes  of  the  brain.  Out- 
breaks of  perspiration  in  certain  circumstances  may  be 
explained  in  similar  ways. 

Summary. — The  salient  facts  regarding  reflex  action 
may  now  be  concisely  stated.  Reflexes  are  adaptive  reac- 
tions brought  about  by  the  influence  of  stimuli  acting 
upon  the  receptors  of  the  nervous  system.  For  their 
execution  five  conditions  must  be  fulfilled:  (1)  The  end- 
organs,  or  receptors,  must  be  ready  to  translate  the 
energy  applied  from  without  into  nerve-impulses.  (2) 
There  must  be  pathways  open  for  the  conduction  of  these 
impulses  to  the  gray  matter  of  the  central  axis.  (3)  The 
central  gray  matter  must  have  such  an  organization  and 
such  a  degree  of  irritability  that  the  arrival  of  the  afferent 
impulses  shall  determine  the  departure  of  efferent  im- 
pulses along  definite  paths.  The  fitness  of  the  reflex  to 
the  emergency,  as  commonly  observed,  is  explained  by  the 
physiologic  linkage  of  certain  afferent  with  certain  efferent 
channels  in  the  cord  and  brain.  (4)  There  must  be  lines 
of  effective  communication  between  the  central  stations 
and  the  end-organs  of  the  efferent  system,  namely, 
muscles  and  glands.  (5)  These  organs  must  be  capable  of 
modifying  their  activity  upon  the  arrival  of  the  outflow- 
ing impulses.  The  change  induced  may  be  in  the  direc- 
tion of  increased  activity  or  the  reverse — excitation  or 
inhibition. 


58      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

These  statements  serve  to  characterize  reflexes  in  a 
positive  fashion.  On  the  negative  side  we  should  empha- 
size their  essential  indcpendent'e  of  mental  life.  We 
note  the  occurrence  of  many  reflexes,  but  our  conscious- 
ness is  a  matter  of  observation  and  not  of  initiation. 
The  abrupt  reflexes  are  "quicker  than  thought,"  while 
those  which  are  gradual  in  their  development  are  usually 
capable  of  passing  through  all  their  stages  without  our 
attending  to  them.  AVhen  the  will  is  enlisted  at  all — if 
we  may  trust  our  own  impressions — it  is  about  as  often 
to  restrain  as  to  advance  the  process  which  we  find  taking 
place.  Nothing  is  harder  for  the  average  student  than 
to  accept  the  view  that  these  acts  witness  only  to  struc- 
ture and  not  to  present  intelligence.  If  the  scientific 
assertion  is  unwelcome,  it  may  still  be  claimed  that  past 
intelhgence  is  registered  in  the  structure  which  works  so 
smoothly.  Holmes  said  that  "habit  is  action  in  the 
present  from  motives  of  the  past";  the  conception  might 
be  broadened  to  cover  the  field  of  the  reflexes.  But  it 
will  be  found  unexpectedly  diflficult  to  defend  even  this 
thesis. 

Voluntary  Reactions. — If  a  man  presses  an  electric  key 
as  soon  as  possible  after  hearing  a  sound,  feeUng  a  contact, 
or  seeing  a  spark,  he  is  said  to  execute  a  voluntary  reac- 
tion, and  the  time  which  intervenes  between  the  stimulus 
and  the  response  is  called  the  reaction-time.  It  is  gener- 
ally not  less  than  0.12  second  nor  more  than  0.2  second. 
The  values  for  different  avenues  of  stimulation  are 
somewhat  characteristic;  for  instance,  the  response  to 
sound  is  more  prompt  than  that  to  sight.  The  process 
difl'ers  from  an  ordinary  reflex  in  requiring  attention  to 
insure  the  movement.  The  path  of  the  nerve-impulses  is 
a  long  one,  lying  partly  in  the  cerebrum  and  probably 
including  many  synapses. 

When  the  lower  eyelid  receives  an  electric  shock  of 
sufficient  strength  there  is  a  wink  which  is  quite  involun- 
tary. This  is  a  reflex  and  it  is  accomplished  within  0.05 
second  of  the  stimulus.    With  a  somewhat  weaker  shock 


REFLEXES  59 

it  is  often  found  that  the  delay  is  three  times  as  long. 
Such  a  case  is  a  voluntary  reaction:  there  is  a  sensation, 
a  purpose  to  wink,  and  then  the  movement.  This  common 
laboratory  experiment  brings  the  two  forms  of  response 
into  clear  contrast.  Consciousness  is  quite  incidental  to  a 
reflex,  and,  if  it  is  involved  at  all,  it  is  subsequent  to  the 
act  and  not  connected  with  the  chain  of  events  leading  up 
to  it. 


CHAPTER   V 

THE  GENERAL  ANATOMY   OF  THE  NERVOUS 

SYSTEM 

It  has  been  possible  to  proceed  to  this  point  with  only 
the  most  general  statement  of  the  spatial  arrangement  of 
the  parts  which  are  united  to  form  the  nervous  system. 
A  certain  amount  of  detail  must  now  be  supplied.  It  will 
be  helpful  to  make  some  comparisons  between  what  is  to 
be  seen  in  the  simpler  vertebrates  and  what  is  found  in 
man.  No  description  of  the  invertebrate  organization 
will  be  undertaken;  it  is  most  interesting  but  peculiarly 
difficult  to  bring  into  line  with  the  higher  type. 

Let  us  attend  to  the  outlines  of  the  nervous  mechanism 
as  exemplified  in  the  frog,  an  animal  which  has  been  chosen 
for  very  many  of  the  cardinal  researches  upon  this  system. 
Here,  as  always,  we  recognize  an  axial  or  central  portion 
and  the  nerves  extencUng  from  it  to  all  parts  of  the  body. 
The  axial  portion  is  said  to  consist  of  the  brain  and  the 
spinal  cord.  The  brain  is  lodged  in  the  cavity  of  the  skull; 
the  cord  extends  through  a  canal  made  by  the  successive 
arches  of  the  vertebrse,  the  individual  bones  of  the  spinal 
column.  Those  nerves  which  take  their  rise  from  the 
brain  are  called  cranial,  the  reference  being  to  the  cranium, 
which  is  the  portion  of  the  skull  bounding  the  brain. 
The  nerves  originating  from  the  cord  are  called  spinal. 
The  cranial  nerves  issue  from  the  skull  through  openings 
which  are  called  foramina.  The  spinal  nerves  find  their 
way  through  notches  between  adjacent  vertebrae,  inter- 
vertebral foramina,  as  they  are  called.  The  number  of 
both  the  cranial  and  the  spinal  nerves  is  smaller  in  the 
frog  than  in  many  of  the  higher  forms,  including  man. 

60 


GENERAL  ANATOMY  OF  THE  NERVOUS  SYSTEM   61 

The  spinal  nerves  emerge  in  pairs  which  are  sym- 
metrically developed.  A  single  member,  right  or  left,  in 
one  of  these  pairs  is  found  to  be  united  with  the  cord  by 
two  roots.  These  are  best  referred  to  as  dorsal  and  ventral, 
the  former  being  nearer  the  skin  of  the  back  and  the 
latter  at  a  greater  depth.  The  relations  referred  to  are 
best  understood  when  presented  in  a  diagram  (Fig.  10). 


Fig.  10. — The  upper  figure  shows  the  spinal  cord  within  the  arch 
of  a  vertebra.  A  pair  of  spinal  nerves  is  shown,  each  nerve  having  a 
dorsal  and  a  ventral  root. 

In  the  lower  figure  the  heavy  enclosure  is  the  dura,  mater,  the 
dotted  line  just  within  is  in  the  position  of  the  arachnoid,  and  then 
comes  the  space  filled  by  the  cerebrospinal  fluid.  The  outhne  of  the 
cord  itself  corresponds  with  the  pia  mater. 


The  same  figure  will  call  attention  to  the  protective  struc- 
tures in  the  vicinity.  Of  these,  the  most  striking  is  the  bony 
arch.  Within  this  is  a  dense  membrane,  the  dura  mater. 
A  much  thinner  membrane  is  applied  to  the  immediate 
surface  of  the  cord  and  is  scarcely  to  be  separated  from  it; 
this  is  the  pia  mater.    Between  the  two  membranes  there 


62      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

is  an  appreciable  space  containing  a  clear,  limpid  liquid, 
the  cerebrospinal  fluid.  Strictly  speaking,  a  third  mem- 
brane, the  arachnoid,  intervenes  between  the  dura  and  the 
fluid,  which  is,  therefore,  said  to  occupy  the  subarachnoid 
space.  The  membranes  with  the  fluid  retained  by  them 
are  collectively  spoken  of  as  the  meninyes. 

The  regular  fashion  in  which  the  spinal  nerves  part 
into  dorsal  and  ventral  roots  might  well  suggest  a  differ- 
ence in  function  corresponding  to  the  anatomic  separation. 
It  has,  in  fact,  been  known  for  about  a  hundred  years  that 
the  dorsal  roots  are  almost  wholly  composed  of  afferent 
fibers  and  the  ventral  roots  even  more  dominantl}'^  of 
those  which  are  efferent.  The  statement  of  this  contrast 
in  function  between  the  roots  of  the  two  sets  is  known  as 
Bell's  law.  The  cranial  nerves  do  not  part  in  this  orderly 
way  into  dorsal  and  ventral  divisions  where  they  join  the 
substance  of  the  brain;  moreover,  they  are  extremely 
unequal  in  size.  Some  are  found  to  be  composed  of 
afferent  fibers,  some  of  efferent,  and  some  of  both  together. 
It  will  be  evident  that  each  spinal  nerve,  if  tested  beyond 
the  point  of  blending  of  its  two  roots,  may  be  expected  to 
show  both  characters.  Most  nerves  are  mixed  in  the 
sense  that  they  contain  fibers  of  both  kinds.  In  the  sum 
of  all  the  nerves  it  is  said  that  the  afferent  fibers  are  dis- 
tinctly more  numerous  than  the  efferent.  In  the  spinal 
nerves  the  difference  is  moderate;  in  the  cranial,  the 
preponderance  of  afferent  fibers  is  overwhelming. 

A  cross-section  of  the  spinal  cord  brings  to  view  several 
features  which  may  be  described  later,  but  at  the  moment 
only  one  of  these  will  be  mentioned.  This  is  the  minute 
central  canal,  a  reminder  that  the  central  nervous  system 
is  to  be  regarded  as  tubular  in  its  fundamental  organiza- 
tion, though  the  walls  of  the  primitive  tube  have  en- 
croached upon  its  cavity  until  the  remaining  space  is 
very  small  compared  with  the  masses  of  white  and  gray 
matter  surrounding  it.  The  slender  central  canal  of  the 
cord  leads  forward  to  a  much  more  conspicuous  series  of 
chambers  in  the  brain.    We  can  now  outline  the  anatomy 


GENERAL  ANATOMY    OF    THE    NERVOUS    SYSTEM       63 

of  this  superior  portion  of  the  system  as  it  is  seen  in  the 
frog. 

Following  the  spinal  cord  to  the  most  anterior  vertebra 
we  find  that  it  is  here  continuous  with  the  tapering  hind 


Olfactory   lobes 

Cerebral 
Hemispheres 

-Diencephalor) 

---  hi'td-hraiT) 
--  Cerebelhn) 

-l Medulla 


Fig.  11. — Above,  the  frog's  brain  is  shown  in  its  dorsal  aspect 
and,  within  a  similar  outline,  its  cavities.  The  two  lateral  ventricles 
are  not  numbered.  The  cavities  extending  into  the  optic  lobes  are 
not  made  black  because  they  are  not  characteristic  of  higher  forms. 

Below  is  the  brain  of  the  rabbit  (dorsal  view),  to  show  how  the 
midbrain  is  nearly  concealed  by  the  large  cerebrum  and  cerebellum. 
(The  scale  of  this  drawing  is  much  smaller  than  that  used  for  the 
frog.) 


end  of  the  brain,  the  medulla,  or  bulb.  The  line  of  demarca- 
tion between  brain  and  cord  is  assumed  to  lie  between  the 
back  edge  of  the  skull  and  the  first  vertebra;  there  is  no 
sudden  change  in  the  appearance  of  the  nervous  axis 


64      THE    XKRVOUS    SYSTEM    AND    ITS   COXSEKVATION 

itself  at  this  lAncc.  If  the  overlying  bone  is  removed  the 
several  divisions  of  the  ])rain  will  appear  somewhat  as  in 
Fig.  11.  The  medulla  widens  from  its  hinder  to  its 
forward  limit  and  the  eye  is  caught  by  a  deep  triangular 
hollow,  opening  in  its  dorsal  surface.  The  apex  of  the 
triangle  is  pointed  back  toward  the  cord.  This  hollow  is 
one  of  the  chaml)ers  of  the  brain,  the  fourth  ventricle. 
Unlike  all  the  other  parts  of  the  series  of  cavities,  this 
one  breaks  the  surface;  the  others  are  completely  sub- 
merged and  to  be  seen  only  after  dissection.  A  thin  roof 
which  partially  covers  the  fourth  ventricle  in  life  is  almost 
invariably  stripped  from  it  in  exposing  the  brain.  The 
central  canal  of  the  cord  opens  out  into  the  fourth  ven- 
tricle at  its  pointed  posterior  extremity. 

Forward  of  the  medulla  are  found  the  two  large,  ovoid 
bodies  which,  with  the  corresponding  ventral  structures, 
are  conveniently  covered  by  the  term  midbrain.  A  channel 
extends  from  the  fourth  ventricle  through  this  region  to 
the  cavities  still  farther  forward ;  it  is  picturesquely  named 
the  aqueduct  of  Sylvius.  We  shall  find  the  midbrain  to  be 
relatively  much  less  prominent  in  the  higher  forms  than 
in  the  frog.  An  alternative  name  for  this  region,  apply- 
ing more  accurately  to  the  dorsal  eminences,  is  the  optic 
lobes. 

In  front  of  the  midl^rain  we  find  in  the  case  of  the  frog 
that  iDy  far  the  larger  part  of  what  remains  is  the  cerebrum 
or  the  cerebral  hemispheres.  We  yet  distinguish,  however, 
a  limited  portion  of  the  brain  between  these  paired  struc- 
tures and  directly  before  the  midbrain  as  the  diencephalon. 
In  the  diencephalon  the  aqueduct  of  Sylvius  expands  into 
a  space  which  is  quite  narrow  when  measured  from  right 
to  left,  but  more  extensive  dorsoventrally.  This  is  the 
third  ventricle.  Each  of  the  cerebral  hemispheres  has 
within  it  a  cavity  which  is  called  a  lateral  ventricle. 
The  total  count  of  four  ventricles  is  arrived  at  by  reckon- 
ing these  two  lateral  chambers,  the  third  in  the  dien- 
cephalon, and  the  fourth  in  the  medulla.  The  lateral 
ventricles  communicate  with  the  third  by  small  passages. 


GENERAL    ANATOMY    OF    THE    NKKVOUS    SVSTIOM       ()5 

At  the  extreme  anterior  end  each  of  tlie  hemispheres  is 
prolonged  into  a  brush-Uke  development  of  nerve-fibers 
which  comes  into  relation  with  the  nasal  lining  on  the 
same  side.  These  extensions  are  usually  termed  the 
olfactory  nerves  and  are  counted  as  the  first  in  the  cranial 
series.  No  other  nerves  come  into  direct  connection  with 
the  cerebrum;  even  the  optic  nerves,  which  are  so  much 
more  important  in  determining  the  reactions  of  the  more 
intelligent  animals,  join  the  parts  just  behind  the  hemi- 
spheres and  affect  them  only  after  the  impulses  have  been 
relayed  or  forwarded.  The  optic  nerves  are  second  in  the 
series  as  we  count  from  before  backward.  Other  cranial 
nerves  emerge  at  short  intervals  behind  the  optic.  It  will 
be  better  not  to  enumerate  them  now,  but  to  speak  of  them 
with  direct  reference  to  the  human  brain  a  httle  later. 

All  the  divisions  which  have  been  described  as  having 
places  in  the  organization  of  the  brain  of  the  frog  can  be 
recognized  in  the  brains  of  the  higher  vertebrates.  Their 
proportionate  development  we  shall  find  to  vary  widely 
from  what  has  been  pictured.  There  is  one  region  only 
hinted  at  in  the  brain  of  the  frog  which  comes  to  be  a  large 
feature  in  many  cases.  This  is  the  cerebellum.  Its  posi- 
tion in  the  frog  is  indicated  by  a  slight  dorsal  growth 
at  the  anterior  margin  of  the  fourth  ventricle. 

We  shall  now  find  it  helpful  to  compare  with  the  brain 
of  the  frog  that  of  the  rabbit,  which  will  show  a  state  of 
things  intermediate  between  what  has  been  described 
above  and  the  human  condition  which  must  be  outlined 
presently.  If  we  ignore  differences  of  absolute  scale 
we  shall  see  at  a  glance  that  the  cerebral  hemispheres  in 
the  rabbit  are  more  massive  than  in  the  frog.  We  shall  see 
also  that  the  cerebellum  has  become  a  part  of  the  brain 
only  less  conspicuous  than  the  hemispheres  themselves. 
We  can  still  discover  between  the  cerebellum  and  the 
cerebrum  the  surface  of  the  midbrain,  but  this  section 
which  was  so  prominent  in  the  frog  has  become  much  less 
so.  It  is  evident  that  a  moderate  additional  increase  in 
the  bulk  of  the  cerebrum  and  cerebellum  would  bring 


GtJ      THE    NERVOUS   SYSTEM    AND    ITS    COxXSERVATION 

these  two  in  contact  and  conceal  the  midbrain  from  view. 
Incidentally  it  may  be  noted  that  in  the  rabbit  the  dorsal 
aspect  of  the  midbrain  is  scored  by  a  cross-fissure,  so  that 
instead  of  the  two  lobes  found  in  the  frog  there  is  a  four- 
fold arrangement.  On  this  account  the  region  in  question 
is  known  as  the  corpora  quadrigemina. 

A  change  in  our  point  of  view  from  dorsal  to  lateral^ 
will  make  it  easier  to  grasp  the  result  of  the  progressive 
development  of  the  cerebrum  and  the  cerebellum.  The 
figure  will  show  how  the  midbrain  is  covered  in  the  process 
and  will  suggest  at  the  same  time  how  the  cerebrum  rolls 
forward  over  the  olfactory  nerves,  and  how  the  cerebellum, 
extending  backward,  overhangs  more  and  more  the 
cavity  of  the  fourth  ventricle.  In  cats  and  dogs  a  stage 
is  reached  at  which  no  glimpse  of  the  midl^rain  can  be 
had  without  forcibly  separating  the  overlying  parts. 

To  understand  the  ordering  of  the  various  divisions  in 
the  brain  of  man  it  is  first  of  all  necessary  to  appreciate 
this  preponderance  of  the  cerebrum  and  the  cerebellum 
over  the  remaining  portions.  But  there  is  another  con- 
dition which  enters  in  to  complicate  the  interpretation. 
This  is  a  bending  of  the  axis  upon  which  the  brain  may  be 
conceived  to  be  built  up.  In  the  frog  a  line  drawn  from 
the  nose  through  the  brain  and  back  to  the  end  of  the 
spinal  cord  will  be  nearly  straight.  In  the  rabl)it  it  is  still 
true  that  the  organization  can  be  referred  to  an  axis  which 
is  substantially  straight.  It  is  very  plain  that  the  attempt 
to  project  a  corresponding  line  from  the  human  nose 
through  the  brain  and  down  the  full  length  of  the  cord 
will  yield  a  curve  suggestive  of  a  fish-hook  (Fig.  12). 

This  bending  of  the  axis  is  developed  in  connection 
with  the  carriage  of  the  head  which  is  appropriate  to  the 
erect  position.  The  lower  animals  generally  travel  along 
the  line  of  their  spinal  columns.  Man  moves  in  a  line 
perpendicular  to  his  spine;  that  is  to  say,  he  walks  and 
gazes  horizontally  while  his  vertebral  axis  is  kept  vertical. 
The  nervous  system  must  be  accommodated  to  this  state 
^  Figure  12,  upper  drawing. 


GENERAL  ANATOMY  OF  THE  NERVOUS  SYSTEM   (37 

of  things.  The  bend  m  its  axis  is  well  indicated  by  an 
outline  of  the  cavities  in  the  human  brain  and  cord. 
The  aqueduct  of  Sylvius  is  inclined  ventrally  from  the 
line  of  the  central  canal  of  the  cord,  and  the  lateral 
ventricles  in  the  cerebral  hemispheres  are  extended 
approximately  at  right  angles  to  this  canal.    The  olfactory 


Fig.  12. — Above  is  the  rabbit's  brain  from  the  left;  below,  the 
human  brain  in  vertical  fore-and-aft  section,  also  viewed  from  the 
left.     The  bent  axis  is  introduced  in  the  lower  figure. 

1,  Cerebrum;  2,  cerebellum;  3,  midbrain;  3d,  corpora  quad- 
rigemina;  3v,  crura  cerebri;  4,  pons;  5,  medulla;  ///,  third  ven- 
tricle, which  is  flanked  by  the  diencephalon;  IV,  foiu-th  ventricle. 


outgrowths  are  also  found  to  be  in  a  plane  perpendicular 
to  the  course  of  the  cord. 

If,  now,  we  make  allowance  for  the  two  conditions  indi- 
cated— the  overwhelming  growth  of  the  cerebrmn  and 
cerebellum  and  the  rather  sharp  crook  in  the  axis — we  shall 
find  it  easy  to  see  that,  after  all,  the  sequence  of  the 


08      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

divisions  in  man  is  the  same  as  in  the  frofr.  It  is  true  in 
both  cases  that  the  medulla  is  the  prolongation  of  the  cord 
within  the  skull.  In  both,  the  fourth  ventricle  practically 
breaks  through  the  "roof"  or  dorsal  surface  of  the  medulla, 
but  in  man  it  is  overhung  by  the  cerebellum.  In  both 
types  the  aqueduct  of  Syhius  leads  through  the  region 
known  as  the  midbrain  and  widens  into  a  third  ventricle 
reckoned  as  the  cavity  of  the  diencephalon. 

In  the  brains  of  the  higher  animals  there  is  a  ventral 
feature  hardly  indicated  in  the  frog,  but  developed, 
gencrall}'  speaking,  in  proportion  to  the  prominence  of  the 
cerebellum.  This  is  the  pons  (pons  varolii),  a  structure 
which  presents  the  appearance  of  an  outgrowth  from  the 
cerebellum  clasping  the  medulla  near  its  anterior  border. 
Of  course,  this  does  not  correctly  describe  the  actual  con- 
nections of  the  region  referred  to,  though  it  is  true  that  it 
contains  many  transverse  fibers  which  pass  into  the 
cerebellum.  It  is  to  be  noted  that  the  cerebellum  is  dis- 
tinctly dorsal  in  position  to  the  main  axis  of  the  central 
nervous  system.  It  may  thus  be  said  not  to  lie  upon  the 
direct  course  of  the  ascending  and  descending  impulses 
which  enter  and  leave  the  cranial  cavity.  So  it  is  possible, 
for  experimental  purposes,  to  remove  the  cerebellum  and 
leave  this  chief  highway  still  open  for  service. 

The  removal  of  the  cerebellum,  with  the  object  of  ob- 
serving the  deficiencies  which  follow  and  so  drawing  in- 
ferences in  regard  to  its  previous  activity,  is  permissible. 
But  the  physiologist  cannot  excise  the  midbrain  or  the 
medulla  for  any  such  purpose,  since  he  would  lose  not 
only  the  influence  of  the  part  withdrawn,  but  would 
check  the  passage  of  impulses  to  and  from  regions  an- 
terior to  the  seat  of  operation.  The  destruction  of  the 
medulla  would  leave  no  line  of  communication  between 
the  cerebral  hemispheres  and  the  trunk. 

A  few  words  may  now  be  said  about  the  distribution 
of  gray  and  white  matter  in  the  central  nervous  system. 
In  the  cord  the  gray  matter  is  internal  and  appears  in  a 
cross-section    in    a   characteristic    form    often    called   an 


GENERAL  ANATOMY  OF  THE  NERVOUS  SYSTEM   ()0 

H-figure.  So  far  as  the  cord  consists  of  white  matter,  it 
can  be  regarded  without  serious  error  as  a  huge  nerve 
conveying  impulses  to  and  from  the  brain.  Its  gray  matter 
serves  to  mediate  simple  reflexes.  Yet  it  must  also  be 
remembered  that  the  gray  matter  may  bear  a  part  in  the 
transmission  of  impulses  from  one  level  to  another.  The 
gray  matter  of  the  cord  shows  two  expansions  in  the  course 
of  its  length,  one  between  the  shoulders  and  one  close  to 
the  lower  end.  It  will  readily  be  inferred  that  these  ex- 
pansions provide  for  the  massing  of  cells  related  respec- 
tively to  the  upper  and  lower  extremities. 

In  the  medulla,  as  in  the  cord,  the  gray  matter  is 
practically  all  internal.  The  H-figure,  however,  ceases 
to  be  distinguishable,  and  instead  there  are  more  or  less 
isolated  clusters  of  nerve-cells  which  in  several  con- 
spicuous cases  are  in  connection  with  cranial  nerves.  A 
large  proportion  of  the  substance  of  the  medulla,  includ- 
ing about  all  of  its  superficial  portion,  is  made  up  of  fibers. 
For  the  most  part  these  run  longitudinally,  but  at  certain 
places,  as  revealed  in  sections,  there  are  many  which 
sweep  from  left  to  right,  and  the  reverse,  crossing  the 
midline. 

In  the  restricted  region  which  we  have  termed  the 
midbrain  we  find  that  the  corpora  quadrigemina  (Fig. 
12,  3d),  the  four  eminences  which  rise  upon  its  dorsal 
aspect,  are  largely  gray  matter.  Within,  the  alternation 
of  the  two  types  is  somewhat  intricate,  but  ventrally  this 
part  of  the  brain  consists  of  fibers.  The  ventral  white 
matter  of  the  midbrain  (Fig.  12,  3v)  is  seen  just  forward 
of  the  pons  for  a  short  distance,  and  it  is  referred  to  under 
the  name  of  the  crura  cerebri.  This  is  translated  "the 
legs  of  the  cerebrum,"  and  the  fact  which  doubtless  sug- 
gested the  odd  name  is  that  we  have  here  a  paired  pedestal 
into  which  the  larger  proportion  of  the  fibers  coming  from 
and  going  to  the  cerebrum  are  compressed.  If  a  crude 
comparison  may  be  admitted,  we  may  liken  the  cerebrum 
to  a  great  bouquet  whose  stems  are  gathered  into  the 
crura. 


70      THE    NERVOUS   SYSTEM    AND    ITS   CONSERVATION 

The  cerebrum  itself  and  the  cerebellum  present  a  con- 
trast to  the  other  portions  of  the  brain  when  studied  with 
regard  to  the  distribution  of  graj-  and  white  matter.  In 
thorn  there  is  a  surface  layer  of  gray  substance,  while  the  in- 
terior— and  by  far  the  larger  part  of  tlie  whole  mass — 
is  made  up,  in  the  main,  of  multitudinous  fibers.  The 
surface  layer  is  called  the  cortex,  the  primitive  meaning 
of  the  word  being  the  bark  of  a  tree.  Certain  submerged 
portions  of  gray  matter  are  found  in  the  midst  of  the 
internal  white  matter  in  both  the  cerebrum  and  the 
cerebellum. 

The  human  cerebrum  consists  of  two  hemispheres, 
between  which  there  is  a  very  deep  longitudinal  fissure. 
The  separation  of  the  two  halves  is  so  marked  that  one 
thinks  of  the  walnut  kernel  with  its  comparatively  slender 
isthmus.  The  comparison  is  faulty,  however,  in  that  the 
cerebral  hemispheres  have  more  than  one  bond  of  union. 
Their  principal  tie  is  to  be  found  at  the  bottom  of  the 
longitudinal  fissure,  and  when  cut  it  appears  in  section  as 
a  white  arch.  It  is  the  corpus  callosum,  a  structure  to 
which  the  physiologists  of  the  seventeenth  century  ascribed 
much  importance.  Several  minor  connections  are  ob- 
served lower  down,  all  adjacent  to  the  third  ventricle. 

In  all  the  higher  animals  the  surface  of  the  cerebrum 
is  much  scored  by  fissures.  These  are  called  sulci,  and  the 
convex  ridges  between  them  are  spoken  of  as  gyri  or  con- 
volutions. Such  a  type  of  organization  evidently  provides 
for  a  much  more  extensive  area  of  cortex  than  would  exist 
otherwise.  Since  cortical  development  stands  in  some 
relation  to  the  intelligence  and  general  rank  of  the  animal 
in  the  scale  of  being,  one  is  disposed  to  look  for  an  espe- 
cially marked  wrinkling  in  the  case  of  man.  The  human 
brain  is,  indeed,  much  more  fissured  than  that  of  the 
rabbit,  but  it  is  not  much  more  so  than  that  of  the  .-.cow. 
The  attempt  to  make  a  great  deal  of  this  feature  yields  but 
little  comfort  (Fig.  13). 

Regions  of  the  surface  of  the  cerebrum  are  usually 
denoted  by  employing  the  names  of  those  cranial  bones 


GENERAL  ANATOMY  OF  THE  NERVOUS  SYSTEM   71 

which  overlie  them.  Thus  we  speak  of  the  frontal,  the 
parietal,  the  temporal,  and  the  occipital  regions  or  lobes. 
The  principle  would  entitle  us  to  refer  also  to  the  sphe- 
noidal and  ethmoidal  areas,  but  these  terms  are  seldom 
heard.  The  word  "lobe,"  often  used  with  reference  to 
these  organs,  is,  perhaps,  somewhat  misleading.  It  sug- 
gests a  degree  of  isolation  more  marked  than  that  which 
actually  obtains.  The  temporal  portion  deserves  this 
designation  more  clearly  than  do  the  others,  since  it  is 


Medulla 
Oblongata 


Fig.  13. — The  human  brain,  from  the  left  (Morrow). 


quite  distinct — set  off  by  a  cleft  of  exceptional  depth,  the 
fissure  of  Sylvius.  On  first  glancing  at  a  figure  of  the 
cerebrum  one  recognizes  which  direction  is  anterior  by  the 
presence  of  the  temporal  lobe,'  pointing  downward  and 
forward  (Fig.  13). 

The  Cranial  Nerves  (Fig.  14). — Twelve  pairs  of  nerves 
are  united  with  the  human  brain.  It  has  already  been 
stated  that  only  one  of  these,  the  pair  mediating  the  sense 
of  smell,  is  joined  directly  to  the  cerebrum.  These  bundles 
of  fibers  entering  the  under  surface  of  the  hemispheres 


72-    THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

constitute  the  shortest  aiul  most  direct  of  all  the  paths 
which  convey  afferent  impulses  to  the  central  stations. 
This  fact  is  dwelt  upon  entertainingly  in  "The  Autocrat 


Fig.  14. — View,  from  below,  of  the  connection  of  the  principal 
nerves  with  the  brain:  /',  The  right  olfactory  tract;  //,  the  left 
optic  nerve;  //',  the  right  optic  tract  (the  left  tract  is  seen  passing 
back  into  i  and  c,  the  internal  and  external  corpora  geniculata);  ///, 
the  left  oculomotor  nerve;  IV,  the  trochlear;  V,  V,  the  large  roots 
of  the  trifacial  nerves;  -] — (-,  the  lesser  roots  (the  +  of  the  right 
side  is  placed  on  the  Gasserian  ganglion);  1,  the  oi)hthalmic;  S,  the 
superior  maxillary;  and  3,  the  inferior  maxillary  divisions;  VI,  the 
left  abducens  nerve;  VII,  VIII,  the  facial  and  auditory  nerves;  IX- 
XI,  the  glossopharyngeal,  pneumogastric,  and  spinal  accessory 
nerves;  XII,  the  right  hypoglossal  nerve;  Ci,  the  left  suboccipital 
or  first  cervical  nerve  (De  Nancrede). 


of  the  Breakfast  Table."^  Considerably  farther  back 
we  find  the  conspicuous  optic  nerves,  the  second  cranial 
pair,  reaching  the  base  of  the  brain  and  appearing  to  cross 

'  Riverside  Edition,  p.  75. 


GENERAL  ANATOMY  OF  THE  NERVOUS  SYSTEM   73 

as  they  meet.  The  feature  thus  produced  is  Uke  an  Enghsh 
X  or  the  Greek  letter  Chi,  whence  it  takes  its  name  of  the 
optic  chiasma.  Close  behind  the  chiasma  a  short  stalk 
depends  from  the  brain  and  is  connected  with  the  "pitu- 
itary body,  an  unpaired  organ  which  is  lodged  in  a  hollow 
of  the  sphenoid  bone. 

The  cranial  nerves  are  of  very  unequal  size  and  func- 
tional importance.  A  large  one  is  the  fifth  {trigeminal), 
which  enters  the  pons  and  thus  serves  as  a  convenient 
reminder  that  four  pairs  of  the  nerves  are  anterior  and 
seven  posterior  to  this  structure.  In  this  trunk  are  con- 
veyed a  great  majority  of  the  afferent  fibers  from  the  face, 
the  front  of  the  eye,  the  linings  of  the  nose  and  mouth, 
and  the  teeth.  It  is  responsible  for  a  large  share  of 
human  suffering.  But  efferent  fibers  are  present  also, 
and  the  chief  muscles  employed  in  mastication  are  gov- 
erned through  their  agency.  The  seventh  cranial  nerve, 
springing  from  the  medulla  just  behind  the  pons,  governs 
the  small  muscles  which  are  responsible  for  facial  expres- 
sion. The  eighth  nerve,  entering  the  central  axis  very 
near  the  seventh,  is  the  auditory,  interesting  not  only  as 
the  pathway  on  which  our  hearing  depends,  but  also  for  the 
part  which  it  plays  in  the  maintenance  of  equilibrium. 

The  tenth  nerve  is  one  to  which  reference  must  often 
be  made.  It  is  called  the  vagus  or  'pneumogastric.  Its 
striking  peculiarity  hes  in  the  fact  that  it  is  not  dis- 
tributed so  largely  to  structures  belonging  to  the  head 
and  neck  as  to  the  organs  of  the  trunk  both  above  and 
below  the  diaphragm.  Hence  its  fibers  are,  as  a  rule, 
much  longer  than  those  of  other  cranial  nerves.  They 
reach  muscular  and  glandular  elements  in  all  parts  of  the 
digestive  system,  while  certain  ones  end  in  the  heart  and 
are  of  particular  interest  because  of  the  role  which  they 
fulfil  in  the  regulation  of  its  beating.  Still  others  come 
into  relation  to  the  larynx.  Many  of  the  vagus  fibers  are 
afferent  and  bring  impulses  from  the  tissue  of  the  lungs, 
from  the  heart,  and  from  other  localities. 

As  to  the  less  conspicuous  nerves  of  the  cranial  series, 


74,    THE   NERVOUS   SYSTEM    AND   ITS  CONSERVATION 

it  is  to  be  noted  that  three  pairs  (the  third,  fourth,  and 
sixth  in  the  enumeration)  are  concerned  in  the  causation 
of  movements  of  the  eyes  and  in  bringing  about  the  adjust- 
ments for  varying  iUumination  and  for  vision  at  different 
distances.  The  six  slender  muscles  which  serve  to  turn 
each  eyeball  in  whatever  direction  we  desire  are  probably 
provided  more  liberally  with  motor  nerve-fibers  than  any 
other  muscles  in  the  bod5^  Our  command  over  them  is 
correspontlingly  perfect;  we  do  not  fall  short  or  (n^ershoot 
the  mark  in  looking  from  one  object  to  another.  If  there  is 
another  instance  of  such  precision  in  control  of  muscles  it 
is  the  case  of  those  which  act  upon  the  cartilages  of  the 
larjaix  in  the  trained  singer. 

Reference:  Lickley,  "The  Nervous  System,"  Longmans,  Green  & 
Co.,  London,  1912. 


CHAPTER  VI 

THE  AFFERENT  PART  OF  THE  NERVOUS  SYSTEM 

The  great  majority  of  the  fibers  which  bear  impulses 
toward  the  central  stations  have  their  receptive  endings 
near  the  surface  of  the  body.  A  minority  come  from 
localities  deeply  submerged  and,  therefore,  subject  to 
stimulation  as  the  result  of  internal  rather  than  external 
conditions.  The  function  of  all  afferent  fibers  is  to  cooper- 
ate in  the  production  of  reflex  responses;  a  certain  propor- 
tion of  them,  in  addition,  carry  to  the  gray  matter  the 
impulses  which  determine  sensation.  With  the  shifting 
of  our  attention  we  are  continually  consigning  to  the  class 
of  reflex  producers  fibers  which  but  must  now  furnished 
us  with  the  data  of  consciousness.  Our  interest  in  sen- 
sation is  so  immediate  and  overwhelming  that  we  tend 
to  underestimate  the  unobtrusive  work  of  those  afferent 
elements  which  at  any  given  moment  are  guiding  sub- 
conscious processes. 

Nerve-fibers  of  the  Skin. — The  human  skin  has  been 
computed  to  have  an  area  of  about  1.7  square  meters. 
It  is  thus  as  large  as  a  rug  3  feet  wide  and  5  feet  long. 
Afferent  fibers  in  enormous  numbers  lead  from  small  sub- 
divisions of  this  large  expanse  and  no  point  upon  it  is  far 
removed  from  nerve-terminals.  Sherrington  has  attract- 
ively compared  the  skin  with  its  nerves  to  the  surface 
of  a  pond  where  many  aquatic  plants  are  growing.  Their 
branching  filaments  are  distinct  from  one  another,  but 
often  overlapped  or  entwined.  When  a  stone  is  thrown 
into  the  pond  it  stirs  most  decisively  the  growth  on  which 
it  directly  falls,  but  other  leaves  and  stems  will  share 
somewhat  in  the  disturbance.  Perhaps  in  some  respects 
the  skin  is  even  more  hke  a  marsh  in  which  the  foot  sinks, 


70,    THE    NERVOUS    SYSTEM    AND   ITS    CONSERVATION 

crushing  the  grasses  on  which  it  is  set  and  at  the  same  time 
pressing  down  an  area  much  larger  than  that  which  it  act- 
ually covers.  It  is  precisely  in  this  way  that  a  pencil 
point  jiresscd  into  the  skin  stimulates  powerfully  the  nerve- 
twigs  just  ])encath  the  selected  spot,  but  extends  its  effect 
to  others  within  a  certain  radius. 

The  nerve-fibers  of  the  skin  take  their  rise  in  part  from 
fine  ramifications  among  its  deeper  cells.  Others  lead 
away  from  special  terminal  organs  of  one  kind  and  an- 
other. These  microscopic  end-organs  (tactile  corpuscles, 
etc.)  have  been  minutely  studied  and  will  be  found  de- 
scribed in  detail  in  works  on  histology.  It  is  needless 
here  to  discuss  the  relation  of  the  several  types  of  nerve 
ending  to  the  several  forms  of  stimulation  to  which  each 
may  respond.  In  the  light  of  what  has  been  said  already 
(Chapter  III)  we  shall  assume  that  only  one  result  can 
follow  the  stimulation  of  a  given  fiber,  whatever  the 
means  employed.  If  we  are  right  in  taking  this  position, 
we  must  conclude  that  the  variety  of  sensations  which 
can  be  elicited  through  the  skin  is  made  possible  by  a 
corresponding  number  of  afferent  pathways. 

We  derive  from  the  skin  at  least  four  kinds  of  sensa- 
tion— pressure,  warmth,  cold,  and  pain.  As  we  have 
accepted,  provisionally  at  least,  the  "Miillerian  prin- 
ciple," we  must  believe  that  a  fiber  which  is  once  found 
to  give  the  sensation  of  pressure  when  it  is  stimulated  can 
never  give  any  other  sensation.  For  the  impulses,  how- 
ever they  ma}^  be  started  on  their  way,  are  of  an  un- 
varying nature  and  take  always  the  same  direction. 
On  their  arrival  within  the  confines  of  the  central  nervous 
system  they  must  produce  over  and  over  the  same  set  of 
effects.  The  only  qualifying  statement  which  should  be 
made  is  that  strong  stimuli  of  any  kind  may,  very  prob- 
ably, initiate  impulses  which  shall  penetrate  farther  than 
those  originated  by  less  intense  applications.  So,  accord- 
ing to  one  theory,  yain  may  be  produced  by  a  sufficiently 
strong  excitation  of  any  afferent  nerve,  its  occurrence  being 
the  sign  of  an  extension  of  the  brain  process  beyond  the 


THE    AFFERENT    PART    OF   THE   NERVOUS   SYSTEM      77 

usual  field.  But  the  more  generally  accepted  view  is 
that  pain  is  a  sensation  for  which  a  particular  nervous 
mechanism  is  requisite  and  that  the  nerves  concerned  can 
give  rise  only  to  painful  sensory  phenomena. 

Experimental  study  supports  the  a  priori  deductions 
in  regard  to  the  multiple  character  of  the  receptor  equip- 
ment of  the  skin.  If  one  applies  to  the  arm  a  heated  rod 
of  glass,  one's  first  impression  is  that  sensations  of  press- 
ure and  temperature — perhaps  of  pain  also — are  produced 
by  stimulation  of  a  single  spot.  But  if  the  trial  is  made 
more  carefully,  employing  a  slender  instrument  for  the 
test  and  avoiding  deformation  of  the  skin,  one  brings  to 
light  what  is  called  the  "punctiform"  distribution  of 
sensibility.  By  this  expression  is  meant  the  existence  of 
particular  areas  of  very  small  size  from  which  particular 
sensations  can  be  aroused,  while  others  cannot. 

It  is  possible  to  mark  off  a  chosen  region  on  any  part  of 
the  surface  of  the  body  and  to  determine  within  its 
boundaries  the  points  which  respond  appropriately  to 
four  forms  of  stimulation  by  the  four  kinds  of  sensation 
enumerated  above.  Four  sets  of  points  can  then  be  indi- 
cated in  color,  and  if  the  cutaneous  map  is  preserved  for  a 
time  the  points  are  found  to  be  permanent.  They  must  be 
situated  just  over  the  endings  of  four  distinct  though  more 
or  less  commingled  sets  of  nerve-fibers.  It  is  now  easy  to 
see  how  more  than  one  kind  of  sensation  may  seem  to  be 
produced  when  the  skin  is  touched.  If  the  object  which 
makes  the  contact  is  rather  blunt,  it  is  certain  to  affect 
one  or  more  pressure-points,  while  it  will  either  give  or 
take  heat  to  such  an  extent  as  to  stimulate  neighboring 
organs  which  are  sensitive  to  temperature  changes. 
The  skin  is  Hke  a  mosaic  so  finely  subdivided  that  a  close 
examination  is  necessary  to  resolve  it  into  its  constituent 
parts. 

We  must  expect  that  stimulation  of  a  selected  ending 
in  the  skin  by  unusual  means  will  give  no  sensation  but  the 
one  proper  to  that  fiber.  It  is,  in  fact,  rather  difficult  to 
excite  a  pressure-point  by  forms  of  stimulation  other  than 


78-    THE    NERVOUS    SYSTEM   AND    ITS    CONSERVATION 

pressure,  but  it  is  not  impossible  to  do  so,  and  the  sensory 
result  is  reported  to  be  still  a  sensation  of  pressure.  A 
better  example  of  perverse  excitation  is  observed  when  a 
spot  previously  found  to  be  affected  by  cold  is  touched  with 
a  rod  which  is  quite  hot.  The  spot  is  found  to  respond  with 
the  only  sensation  which  can  possibly  result  from  its 
stimulation,  namely,  that  of  cold.  So  wlien  any  area  large 
enough  to  include  both  warm  and  cold  spots  is  brought 
into  contact  with  something  hot,  the  sensation  has  a 
mixed  character  and  may  be  discovered  to  contain  recog- 
nizable elements  of  warmth  and  cold.  Indeed,  the  tingle 
which  we  call  "cold"  may  be  so  prominent  that  for  a 
moment  we  think  that  the  object  has  a  low  instead  of  a 
high  temperature. 

All  the  afferent  fibers  from  the  skin  are  gathered  into  the 
many  small  nerves  which  are  found  in  all  parts  of  the  body, 
and  these  in  their  turn  unite  with  others  until  the  total 
number  of  the  trunks  is  small  and  their  average  size  con- 
siderable. In  these  larger  nerves,  as  has  been  said  before, 
efferent  as  well  as  afferent  fibers  are  present.  If  we  ex- 
clude for  the  moment  the  afferent  nerves  of  the  head,  we 
shall  find  the  remaining  fibers  of  this  description  parting 
from  their  efferent  fellows  when  the  cord  is  closely  ap- 
proached and  forming  the  dorsal  roots  as  they  pass  in 
between  the  vertebrae.  Upon  these  roots  there  are  ob- 
served to  be  enlargements,  the  dorsal  root  ganglia,  and 
microscopic  study  shows  that  these  contain  the  peri- 
karya  connected  with  the  fibers  passing  through.  As 
stated  in  Chapter  III,  these  are  of  an  oval  outline,  are 
situated  on  side  branches  from  their  respective  fibers,  and 
they  are  not  provided  with  the  ordinary  short,  branching 
dendrites. 

Before  the  division  into  dorsal  and  ventral  roots  is 
reached  the  afferent  fibers  from  the  surface  of  the  body  will 
have  been  joined  by  a  smaller  but  still  immense  number 
from  deeper  regions.  Some  attention  must  shortly  be  given 
to  fibers  of  this  class.  It  is  evident  that  the  stimuli  to 
which  they  are  subject  must  be  chiefly  internal    rather 


THE   AFFERENT    PART    OF   THE    NERVOUS    SYSTEM      79 

than  external.  Yet  they  are  not  altogether  so.  Strong 
pressures  acting  from  without  produce  effects  not  limited 
to  the  skin,  but  extending  to  the  underlying  muscles  and 
to  other  tissues.  Muscles,  tendons,  and  joints  return  to 
the  central  nervous  system  a  host  of  impulses,  the  results 
of  which  are  effective  chiefly  in  producing  adaptive  re- 
flexes, but  also  to  some  extent  in  consciousness. 

The  afferent  fibers,  whatever  their  origin,  enter  the 
spinal  cord  well  around  toward  its  dorsal  fissure,  and 
then,  as  a  rule,  each  divides  into  an  ascending  and  a  de- 
scending branch.  The  descending  branches  are  said  not  to 
run  far  before  they  terminate  among  the  cell-bodies  of  the 
spinal  gray  matter,  doubtless  by  synapses,  through  which 
reflexes  may  be  brought  about.  The  ascending  branches 
may  run  unbroken  to  the  medulla  or  they  may  end  in  the 
gray  matter  of  the  cord.  At  intervals  along  their  course 
the  branches  of  both  orders  have  short  lateral  extensions 
by  which  they  establish  intercourse  with  other  neurons. 
The  arrangement  has  already  been  sketched  in  connection 
with  the  discussion  of  reflexes  (see  page  50). 

If  incoming  impulses  are  to  call  forth  the  more  elabor- 
ate reflexes,  and  especially,  we  believe,  if  they  are  to  give 
rise  to  sensations,  they  must  reach  the  cerebrum.  The 
pathway  thither  is  imperfectly  known  and  not  of  the  first 
importance  in  a  work  like  the  present.  It  has  just  been 
said  that  some  afferent  fibers  actually  reach  the  medulla; 
those  which  have  come  from  the  feet  and  have  this 
anterior  reach  are  the  longest  of  all  neurons.  There  is 
reason  to  think  that  much  of  the  conduction  to  the  brain 
is  accomplished  through  shorter  neurons  in  a  tandem 
arrangement  rather  than  over  these  long,  uninterrupted 
channels.  When  the  medulla  is  attained  in  either  way,  its 
own  cells  are  supposed  to  take  up  the  task  of  transmission. 
These  are  responsible  for  the  forwarding  of  impulses  to 
the  important  intermediate  stations  which  flank  the  third 
ventricle  and  are  known  as  the  optic  thalami.  From  these 
occurs  the  radiation  to  the  cortex  itself. 

Sensations    are    apparently    the    psychic    accompani- 


80.     THE    NKRVOrS    SYSTKM    AM)    ITS    rONSKHVATION 

nicnts  of  certain  processes  in  the  cerebral  j>;ray  matter. 
We  must  assume  that  the  streams  of  energy  flashing  from 
point  to  point  in  the  cortex  arc  very  numerous,  and  we 
cannot  say  why  some  are  attended  with  corresponding 
phenomena  in  our  consciousness  while  others  are  not. 
The  problem  of  attention  is  suggested  at  once,  and  this 
belongs  to  the  psychologist.  For  the  physiologist  it  is  a 
persistent  mystery  how  the  physical  mechanism  can  be  so 
multifarious  and  the  su])jective  experience  so  unified. 

The  afferent  fibers  which  have  thus  far  been  discussed 
are  those  originating  below  the  head.  These  exert  direct- 
ing influences  upon  the  central  mechanism  which  we  are 
not  likely  to  overestimate,  but  their  contribution  to  the 
current  of  sensation  is  much  less  vivid  and  interesting  than 
that  furnished  by  way  of  the  cranial  nerves.  If  there  is  a 
partial  exception  to  be  conceded,  it  is  in  the  case  of  the 
fingers,  with  their  wonderful  sensory  equipment.  Other- 
wise it  needs  no  argument  to  prove  the  superior  prominence 
of  the  eye  and  the  ear  in  guiding  intelligent  conduct.  To 
be  without  taste  or  smell  would  be  a  minor  privation,  but 
deafness  and  blindness  are  grave  calamities,  and  when  the 
two  are  conjoined  we  regard  the  victim  with  a  pitying  awe, 
which  may  be  displaced  by  reverent  admiration  when  we 
witness  such  triumphant  emergences  as  those  of  Laura 
Bridgman  and  Helen  Keller. 

Something  has  been  said  previously  of  the  afferent 
service  of  the  cranial  nerves.  It  will  ))e  recalled  that  in 
these  nerves  there  is  no  clear  assorting  of  sensory  fibers  to 
form  a  series  of  dorsal  roots.  In  two  or  three  cases  there 
are  ganglia  in  which  are  gathered  the  perikarya  which 
maintain  the  passing  fibers.  The  largest  of  these  ganglia 
and  the  one  most  frequently  referred  to  is  the  Gasserian 
ganglion  on  the  trunk  of  the  great  fifth  (trigeminal) 
nerve. 

Vision. — The  immense  importance  of  the  optic  impulses 
in  determining  the  content  of  the  human  mind  and  the 
conduct  of  human  life  is  faithfully  indicated  in  the  large 
size  of  the  optic  nerves.    Nearly  half  a  million  fibers  are 


THE   AFFERENT    PART    OF   THE    NERVOUS    SYSTEM      81 

bound  up  in  one  of  these,  most  massive  of  all  purely  affer- 
ent trunks.  It  has  been  stated  elsewhere  that  the  imme- 
diate connections  made  by  the  optic  fibers  are  with  stations 
in  the  midbrain  or  thereabouts.  From  these  subordinate 
centers  reflexes  are  doubtless  caused,  while,  at  the  same 
time,  impulses  mount  to  the  cortex  where  the  processes 
induced  become  the  physical  basis  of  conscious  vision. 

Hearing. — The  number  of  fibers  concerned  in  carrying 
the  impulses  on  which  the  sense  of  hearing  depends  is 
small  compared  with  that  of  the  optic  conductors.  It 
has  been  estimated  that  perhaps  14,000  fibers  on  each 
side  are  provided  to  subserve  this  function.  The  sound- 
waves which  have  come  pulsing  through  the  air  to  the 
external  ear  communicate  their  motion  to  a  succession 
of  structures  in  the  winding  cavities  of  the  temporal  bone, 
and  ultimately  to  cells  which  can  transmute  this  mechan- 
ical energy  to  the  form  of  nerve-impulses.  The  result- 
ing currents  are  led  to  gray  matter  within  the  medulla, 
forwarded  thence  to  the  midbrain,  and  finally,  by  a  third 
relay,  to  the  cerebral  cortex. 

The  auditory  nerve  has  a  second  part  which  is  not  sup- 
posed to  have  to  do  with  hearing.  This  division,  the 
vestibular  nerve,  brings  to  the  brain  impulses  which  have 
been  started  by  displacements  of  fluids  or  of  solid  particles 
in  the  comparatively  large  portion  of  the  internal  ear 
which  is  looked  upon  as  an  organ  of  equilibration.  There 
is  reason  to  believe  that  when  one  sways — or,  more  radi- 
cally, when  one  stumbles — such  mechanical  disturbances 
are  brought  about  and  impulses  sent  to  the  proper  centers 
to  dictate  the  compensating  movements  which  are  so 
promptly  observed.  The  service  of  the  ear  in  maintain- 
ing the  balance  is  one  which  we  seldom  think  of,  and  it  is 
carried  on  for  the  most  part  with  only  slight  involve- 
ment of  sensation.  But  excessive  stimulation  of  the  in- 
ternal ear  probably  has  a  share  in  developing  the  disagree- 
able feeling  we  call  vertigo. 

Taste  and  smell  are  two  kinds  of  sensation  which  are 
often  blended  in  our  experience,  but  the  nervous  paths 
6 


82-     THE    NERVOUS    SYSTEM    A\D    ITS    COXSEUVATION 

concerned  are  widely  separated,  as  the}^  run  from  the 
receptors  to  the  central  apparatus.  The  olfactory  fillers, 
as  we  have  seen  before,  plunge  into  the  under  surface  of 
the  cerebrum  itself.  The  fibers  on  which  taste  depends 
are  probably  scattered  in  the  trunks  of  two  or  three 
nerves,  and  their  arrangement  is  thought  to  be  subject  to 
a  good  deal  of  individual  variation,  ])ut  it  is  certain  that 
their  place  of  entrance  into  the  su])stance  of  the  brain 
is  far  back  of  that  for  the  impulses  from  the  organ  of 
smell. 

Sensations. — We  are  now  in  a  position  to  make  some 
general  statements  based  on  the  outlines  of  the  afferent 
system  which  have  been  given.  It  is  evident  that  chan- 
nels to  the  number  of  millions  exist  by  which  the  central 
nervous  system  may  be  approached  from  without.  The 
impulses  moving  along  these  pathways  may  have  been 
started  by  changes  in  mechanical  relations  at  the  nerve- 
endings  (pressure,  tension,  vibration).  In  certain  cases 
they  may  be  the  result  of  temperature  changes,  either 
elevations  or  depressions.  In  other  instances,  including 
the  action  of  the  organs  of  taste,  smell,  and  vision,  the 
immediate  source  of  the  impulses  must  be  described  as  a 
chemical  change.  However  they  may  originate,  the 
biologic  function  of  all  these  inflowing  currents  is  to 
determine  adaptive  reactions  of  the  reflex  tj^pe. 

But  as  human  beings  we  find  the  sensations  which 
are  associated  with  the  arrival  of  certain  of  these  im- 
pulses of  the  greatest  interest.  Either  intensity  or  novelty 
of  stimulation  will  be  likely  to  insure  an  echo  in  conscious- 
ness. We  are  usually  quite  ignorant  of  the  state  of  most 
of  our  internal  organs;  this  does  not  mean  that  no  im- 
pulses are  ascending  from  them  to  the  brain,  but  rather 
that  these  impulses  have  a  monotonous  character.  Foster 
is  responsible  for  the  assertion  that  we  should  instantly 
miss  the  sensory  contribution  of  the  viscera  if  it  should 
cease.  To  put  the  proposition  somewhat  crudely,  we  may 
say  that  we  have  no  sensations  from  the  alimentary  canal, 
but  we  should,  in  all  probability,  realize  a  difference  if  it 


THE    AFFERENT    PART    OF   THE    NERVOUS   SYSTEM      83 

were  suddenly,  though  painlessly,  removed.  The  back- 
ground of  consciousness  would  be  altered;  visceral  sensa- 
tion might  be  hkened  to  the  mountain  range  on  the 
horizon,  the  constant  presence  of  which  would  not  dis- 
tract attention  from  the  domestic  action  in  the  foreground, 
though  its  disappearance  would  be  something  uncanny 
and  appalhng. 

Sensations  are  commonly  divided  into  two  groups — 
the  general  and  the  special.  General  sensations  are  those 
which  are  referred  to  the  varying  conditions  of  the  body 
itself;  special,  to  causes  external  to  ourselves.  Normal 
visual  sensation  is  clearly  of  the  special  class.  This  is 
true  also  of  hearing,  smell,  and  taste.  (It  should  hardly 
be  necessary  to  say  that  matter  in  the  nasal  or  mouth 
cavity  is  not  truly  within  the  body,  but  only  in  contact 
with  a  portion  of  its  surface.)  Sensations  from  the 
skin,  as  pressure,  warmth,  cold,  and  cutaneous  pain,  are 
conveniently  regarded  as  special,  on  the  theory  that 
something  is  acting  from  without  to  give  rise  to  them. 
Yet  it  may  be  noted  that  we  very  readily  change  our 
subjective  attitude  toward  some  of  these  experiences. 
We  may  say  that  we  are  warm  or  that  the  room  is  warm, 
shifting  the  reference  in  the  most  facile  way  between  the 
external  world  and  the  body  itself. 

General  sensations  are,  for  the  most  part,  disagreeable, 
a  fact  which  one  is  inclined  to  connect  with  their  common 
relation  to  conditions  which  call  for  correction.  If  hunger 
and  thirst  were  pleasant  to  experience  they  would  not 
impel  us  to  take  measures  for  their  banishment.  Of 
course,  this  is  true  of  pain  in  general,  though  the  remedy 
may  not  be  so  obvious.  So  largely  do  the  general  sensa- 
tions belong  to  maladjustments  that  it  has  been  suggested 
that  the  measure  of  health  is  to  be  found  in  the  extent 
to  which  they  are  crowded  out  by  the  special.  A  man  who 
is  extremely  ill  may  have  little  margin  for  attending  to 
what  he  sees  and  hears;  bodily  discomfort  may  almost 
completely  monopolize  his  attention.  A  man  who  is  ex- 
ceptionally well  has  little  occasion  to  dwell  on  sensations 


84  ■    THE   NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

of  the  general  class.    A  simple  diagram  may  serve  to  give 
vividness  to  this  contrast  (Fig.  1.5). 

The  transition  from  a  condition  in  which  special  sensa- 
tions fill  the  field  of  the  attention  to  one  in  which  they  have 
become  decidedly  a  minor  matter  may  be  quite  precipitate. 


Fig.    15. — The  encroachment  of  the  general  sensations  upon  the 
special  in  transition  from  health  to  sickness. 

Consider,  for  example,  the  voyager  upon  the  deck  of  a 
steamer.  At  one  moment  we  see  him  engrossed  by  the 
beauty  of  the  sea  and  skj'-,  the  freshness  of  the  breeze 
against  his  face,  and  the  tingle  of  the  pure  air  in  his 
nostrils.  After  a  very  brief  interval  he  may  be  found 
utterly  absorbed  by  one  horrible  general  sensation. 


CHAPTER  VII 

THE  NEUROMUSCULAR   MECHANISM 

The  most  conspicuous  manifestations  of  the  activity 
of  the  nervous  system  are  the  contractions  of  the  skeletal 
muscles.  Locomotion,  balancing,  movements  of  the  arms 
and  hands,  changes  of  facial  expression,  speech — all  these 
are  examples.  So  also  is  breathing,  a  rhythmic  process 
which  we  are  apt  to  regard  as  similar  in  its  nature  to  the 
beating  of  the  heart,  but  which  is  fundamentally  differ- 
ent, inasmuch  as  every  breath  is  the  sign  of  an  outflow  of 
nerve-impulses  from  the  central  gray  matter,  while  the 
heart  beats  as  a  result  of  its  own  intimate  properties. 

Each  skeletal  muscle  has  a  supply  of  efferent  fibers. 
It  has  also  afferent  connections  which  are  of  much  im- 
portance, though  usually  overlooked.  A  large  muscle, 
like  the  biceps  in  the  upper  arm,  can  be  recognized  to 
consist  of  numerous  parallel  bundles  set  apart  by  connect- 
ive tissue.  These  bundles,  in  their  turn,  can  be  resolved 
into  more  slender  prismatic  subdivisions,  and  the  finest 
visible  ''grain"  is  perhaps  the  indication  of  the  fibers  which 
are  the  working  units  of  the  mechanism.  A  typical 
muscle-fiber  is  of  hair-like  proportions,  being  an  inch  or 
two  in  length  and,  on  an  average,  about  t^-q  inch  in 
diameter.  Each  of  these  fibers  may  be  regarded  as  a 
muscle  in  miniature  and  has  its  own  nervous  connection. 

It  must  not  be  inferred  that  the  number  of  motor  fibers 
in  the  nerves  is  equal  to  the  number  of  muscle-fibers  sup- 
plied. A  single  nerve-fiber,  as  it  approaches  its  termina- 
tion within  the  muscle,  branches  rather  freely  and  is  thus 
linked  to  a  considerable  number  of  muscle-fibers.  It 
may  govern  as  many  as  one  hundred  or  the  number  may 
be  much  smaller.     Muscles  which  are  under  the  most 

85 


80      THE   NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

precise  voluntary  control  have  an  exceptionally  liberal 
apportionment  of  motor  nerve-fibers.  Such  is  the  case 
with  the  little  muscles  which  rotate  the  eyeball,  executing 
movements  over  which  we  have  the  most  complete  com- 
mand. Doubtless  the  small  muscles  which  act  upon  the 
vocal  cords  have,  as  already  noted,  a  relatively  large 
number  of  nerve-fibers  by  which  their  eminently  skilled 
action  is  determined. 

Each  motor  fiber  proceeds  from  a  perikaryon  which  may 
be  in  the  lower  sections  of  the  brain  if  the  destination  is  a 
muscle  of  the  head,  but  which  will  be  in  the  spinal  gray 
matter  if  the  muscle  is  in  the  trunk  or  limbs  (see  page  33. 


Fig.  16. — A  "neitromusciilar  unit"  as  defined  in  the  text.  The 
motor  perikaryon  is  united  through  its  branched  fiber  and  end- 
plates  with  five  muscle-fibers.  The  typic  number  would  be  much 
larger. 

Every  perikaryon  so  situated  is  evidently  in  a  position 
to  bring  into  action  a  moderate  number  of  muscle-fibers 
if  it  is  itself  stimulated.  A  center  for  a  muscle,  to  be 
worthy  of  the  name,  should  consist  of  many  perikarj^a  so 
enchained  as  to  act  simultaneously  upon  the  contractile 
units  of  the  muscle,  leaving  none  of  them  unstimulated. 
A  fact  to  be  borne  in  mind  is  that  the  fibers  of  skeletal 
nmscle  cannot  communicate  the  contractile  process  from 
one  to  another.  They  are  insulated  units  and  their 
coordination  must  be  secured,  if  at  all,  by  the  manner 
in  which  the  motor  perikarya  of  the  gray  matter  are 
assembled. 


THE    NEUROMUSCULAR    MECHANISM  87 

The  muscle-fiber  has  been  said  to  be  the  working 
unit  of  a  muscle.  A  motor  perikaryon,  with  its  long  axon 
extending  to  the  muscle,  branching  at  last  and  joining 
a  cluster  of  muscle-fibers,  may  be  looked  upon  as  the 
neuromuscular  unit  (Fig.  16).  In  this  combination  there 
is  a  set  of  structures  not  yet  described.  The  reference  is 
to  the  intermediate  elements  between  the  nerve-fibers 
at  their  terminations  and  the  protoplasm  of  the  muscle. 
These  mediating  structures  are  called  motor  end-plates, 
and  they  have  characters  which  differentiate  them  both 
from  nerve  and  muscle.  They  must  be  transmitters  of 
the  excitatory  process  from  the  nerve-fibers  to  the  muscle- 
fibers,  and  the  interest  felt  in  them  springs  from  the  fact 
that  they  conduct  with  very  variable  facility  under 
changing  conditions. 

The  simplest  conceivable  reflex  finding  expression 
through  skeletal  muscle  would  be  realized  in  case  a  single 
afferent  fiber  were  stimulated  and  its  influence  concen- 
trated upon  the  dendrites  of  a  single  motor  neuron. 
The  resulting  flutter  of  a  few  muscle-fibers  buried  among 
thousands  of  their  fellows  in  a  muscular  mass  could  hardly 
be  discerned.  The  most  restricted  reflex  which  we  can 
observe  doubtless  involves  a  fairly  large  number  of 
motor  neurons  with  their  dependent  muscle-fibers.  More- 
over, it  is  supposed  that  adjustor  or  association  neurons 
almost  always  intervene  in  the  directing  of  the  impulses. 

In  the  present  chapter  it  is  intended  to  advance  from 
the  discussion  of  the  simple  reflex,  already  familiar  in 
principle,  to  instances  of  motor  performance  which  are 
commonly  held  to  lie  outside  this  class.  One  thinks 
immediately  of  the  so-called  "voluntary"  movements. 
It  has  previously  been  stated  that  there  is  no  clear  de- 
marcation between  the  two  varieties.  The  more  care- 
fully one  analyzes  the  conditions  surrounding  each, 
the  less  distinction  there  seems  to  be.  A  reflex  move- 
ment is  one  occurring  prompt^  and,  as  a  rule,  inevitably 
in  response  to  a  change  of  external  conditions.  A  volun- 
tary movement  is  also  an  adjustment  depending  upon 


88      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

external  conditions,  though  some  of  the  factors  deter- 
mining it  may  He  far  in  tlie  past.  It  is,  of  course,  an  act 
of  which  one  is  conscious  and  which  one  desires  to  see 
taking  place.  It  is  more  profitable  to  attempt  to  unravel 
the  phj^sical  mechanism  than  to  enter  the  metaphj''sical 
discussion  which  is  suggested. 

Movements  of  the  muscles  which  are  closely  associated 
with  our  consciousness  and,  as  it  seems  to  us,  directed  by 
it  are  brought  to  pass  by  neurons  having  their  perikarya 
in  the  cortex  of  the  cerebrum.     The  fibers  belonging  to 


Fig.  17. — Here  a  "neuromuscular  unit"  like  that  in  Fig.  16  is 
shown  under  the  sway  of  a  cortical  motor  cell  (b).  The  "projection 
fiber"  from  this  cell  crosses  the  midplane  of  the  body  as  suggested 
by  the  line  rti.  In  reality,  a  typic  cortical  cell  probably  influences  a 
number  of  cells  of  the  lower  order. 


such  neurons  never  pursue  an  unbroken  course  to  the 
muscles  which  they  can  call  into  action,  but  run  down  to 
form  synapses  with  nerve-elements  of  the  type  already 
mentioned,  which  are  either  near  the  place  of  origin  of 
those  cranial  nerves  which  contain  motor  fibers  or  else  in 
the  spinal  gray  matter.  The  fibers  which  transmit  im- 
pulses from  the  cortex  to  the  neurons  directly  presiding 
over  the  muscles  belong  to  the  class  called  projection 
fibers.  An  odd  peculiarity  of  these  is  that,  as  they  descend, 
they  generally  cross  the  midplane  of  the  nervous  system 


THE    NEUROMUSCULAR    MECHANISM  89 

and  finally  enter  into  relations  with  the  motor  apparatus 
on  the  opposite  side  of  the  body  (Fig.  17). 

The  typic  relation  of  skeletal  muscles  to  the  nervous 
system  having  been  indicated,  three  subjects  now  sug- 
gest themselves  for  discussion  in  some  detail.  These  are 
the  gradation  of  responses,  coordination,  and  neuro- 
muscular fatigue. 

Gradation  of  Responses. — It  is  a  famihar  but  none  the 
less  a  wonderful  thing  that  we  so  successfully  adapt  our 
muscular  efforts  to  the  purposes  which  they  are  designed 
to  serve.  If  one  raises  a  book  from  the  table  one  does  not 
fling  it  upward  with  useless  excess  of  energy,  nor  does  one 
waste  much  time  in  preliminary  contractions  which  do  not 
suffice  to  move  it.  Unless  one  is  deceived  in  his  estimate 
of  the  weight  to  be  handled,  there  is  evidence  of  the  most 
admirable  economy  in  the  execution  of  the  movement. 
Judgment  may  sometimes  be  found  at  fault,  as  when  a 
bottle  of  mercury  resists  so  surprisingly  the  attempt  to 
lift  it  or,  in  the  opposite  fashion,  when  an  empty  box  is 
picked  up  by  one  who  has  been  handling  a  series  of  boxes 
which  were  heavy. 

How  this  grading  of  contractions  to  their  uses  is  brought 
about  is  not  entirely  clear.  In  all  probability,  a  vigorous 
voluntary  effort  means  a  cerebral  process  which  is  com- 
paratively widespread  and  intense  in  degree.  A  small 
movement,  or  the  sustaining  of  a  trifling  weight,  may 
mean  a  less  intense  or  a  more  localized  process,  or  it  may 
mean  both.  If  intensity  is  what  counts,  we  may  assume 
that  whether  a  contraction  made  by  a  given  muscle 
is  great  or  small,  the  number  of  projection  fibers  em- 
ployed to  bring  it  to  pass  is  the  same.  On  the  other 
hand,  it  is  interesting  to  consider  the  second  possibility, 
that  is,  that  a  contraction  will  be  large  if  the  number  of 
neuromuscular  units  cooperating  to  produce  it  is  large, 
and  reduced  in  proportion  to  the  reduction  of  the  number 
of  these  units  engaged.  Keith  Lucas,^  of  Cambridge, 
England,  is  the  physiologist  to  whom  we  owe  the  second 
1  Journal  of  Physiology,  1905,  xxxiii,  125;  1909,  xxxviii,  113. 


90      THE    NERVOIS   SYSTEM    AND    ITS    COXSERVATION 

conception.  Though  it  seems  at  first  to  be  rather  difficult 
to  entertain,  we  shall  find  that  a  strong  case  can  be  made 
for  it. 

If  every  muscle-fiber  is  comparable  with  a  rcpeatino; 
firearm  in  which  new  annnunition  is  rapidly  i)laced  in 
position  to  be  discharged,  it  is  hard  to  see  how  a  stimulus 
strong  enough  to  have  any  effect  can  do  less  than  discharge 
all  the  energy  which  can  possibly  be  released  at  the 
moment.  If  a  blast  is  to  be  fired,  it  is  immaterial  whether 
a  small  or  a  large  spark  is  used  for  the  purpose.  This  is 
precisely  the  case  with  the  heart.  The  form  of  muscular 
tissue  composing  the  walls  of  this  organ  is  said  to  obey 
the  "all-or-none  law,"  by  which  we  mean  that  none  but 
full-sized  contractions  can  be  obtained  from  it. 

It  is  the  conception  of  Lucas  that  the  isolated  fiber  of 
skeletal  muscle  would  be  found  to  conform  to  the  all-or- 
none  principle  if  we  could  make  experiments  upon  it. 
The  real  difference  between  such  fibers  and  those  of  the 
heart,  he  supposes,  lies  in  the  insulated  character  of  the 
former  and  the  protoplasmic  union  of  the  latter.  A 
process  of  contraction  once  started  in  the  heart  will 
usually  sweep  over  all  the  })undles  which  make  up  its 
substance.  In  skeletal  nuiscle  such  a  process  is  definitely 
limited  to  the  units  actually  reached  by  nerve-impulses, 
and  a  maximal  response  cannot  be  secured  unless  the 
stimulation  can  be  made  to  affect  every  fiber  through  its 
end-plate.  A  stimulation  of  only  a  certain  proportion 
of  the  units  will  result  in  a  movement — or  a  tension — at 
the  tendon  less  than  the  maximum.  Because  the  number  of 
units  is  large  the  number  of  possible  gradations  lietween 
the  least  and  the  greatest  will  be  correspondingly  large. 

The  idea  set  forth  by  Lucas  can  be  expressed  in  other 
words.  It  makes  what  we  call  a  muscle — assuming  unity 
of  action  for  all  the  fibers  which  can  act  upon  a  common 
tendon — a  fnuscidature,  that  is,  a  sj^stem  capable  of  more 
or  less  localized  action  at  some  times  and  of  a  mutual 
reinforcement  among  all  its  parts  when  all  its  powers  are 
called  in  play.     When  we  venture  to  speak  of  a  muscle 


THE   NEUROMUSCULAR    MECHANISM  91 

as  though  it  were  necessarily  integral  in  its  nature,  we  may 
be  taking  an  unwarranted  liberty. '^  The  objection  to 
this  view,  that  a  muscle  containing  some  active  and  some 
idle  elements  should  give  evidence  of  the  fact  by  its 
general  appearance,  is  not  a  weighty  one.  A  muscle  which 
is  maintained  in  a  prolonged  contraction  probably  pre- 
sents an  intricate  picture  of  alternating  activity  among 
its  fibers.  If  we  could  distinguish  what  is  going  on  we 
might  see  hundreds  of  these  shortening,  while  correspond- 
ing numbers  might  be  relaxing.  The  net  result  of  rhyth- 
mic action  on  the  part  of  vast  numbers  of  units,  providing 
that  they  keep  "out  of  step,"  may  well  be  to  give  a  gross 
impression  of  constant  shortening.  This  is  precisely  the 
explanation  offered  by  Lingle^  for  the  continuous  or  "tonic" 
contraction  observed  in  the  alimentary  canal. 

If  we  adopt  the  description  of  the  muscular  mechanism 
given  above,  we  can  accept  Lucas'  theories  entirely,  and 
shall  assume  that  a  small  movement  is  one  to  produce 
which  only  a  small  percentage  of  the  available  fibers  are 
put  into  simultaneous  contraction,  while  a  large  one  is  the 
external  sign  of  the  more  general  participation  of  the 
fibers.  The  experimenter  sometimes  sees  indications  of 
localized  responses  in  skeletal  muscle,  and  more  attention 
to  this  matter  is  greatly  to  be  desired.  It  is  certain  that 
if  there  is  any  failure  of  the  nerve-cells  to  act  when  a  muscle 
contraction  is  being  sustained,  there  will  be  unemployed 
fibers  in  the  muscle.  We  readily  grant  that  the  power 
developed  by  physical  training  is  partly  due  to  increased 
ability  to  make  groups  of  muscles  act  together,  and  it  does 
not  seem  unhkely  that  there  is  such  a  thing  as  an  intra- 
muscular coordination  which  has  to  be  secured. 

Many  interesting  considerations  follow  the  admission 
that  muscles  may  act  fractionally.  It  becomes  quite  pos- 
sible that  a  part  of  the  resources  represented  may  not  be 
within  reach  of  our  usual  deliberate  control.     Such  inac- 

^  Gertrude  F.  Barbour  and  the  author  in  American  Physical 
Education  Review,  February,  1912. 

2  American  Journal  of  Physiology,  1910,  xxxvi,  361. 


92      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

cessible  units  may  be  thrown  into  action  in  a  reflex  fashion 
or  when  the  cerebral  processes  are  of  an  exceptional  char- 
acter, as  in  strong  emotion,  hypnosis,  delirium,  and  the 
like.  These  states  are  often  occasions  for  the  most  aston- 
ishing display  of  strength.  This  is  the  more  surprising 
because  the  subjects  are  not  necessarily  athletic  or  even 
of  average  muscular  development.  Surely  in  the  case  of  a 
man  wasted  by  fever  we  have  no  right  to  assume  a  superior 
condition  of  the  muscles  themselves.  If  such  a  man  sud- 
denly becomes  violent  and  masters  attendants  whom  he 
could  not  handle  when  in  his  normal  condition,  it  is  most 
natural  to  infer  that  his  peculiarity  consists  in  a  more 
complete  power  to  command  his  limited  muscular  re- 
sources than  is  realized  at  other  times. 

Other  possible  explanations  may,  nevertheless,  suggest 
themselves.  The  capacity  of  muscles  to  respond  to  the 
stimulation  proceeding  from  the  central  nervous  sj'^stem 
depends  in  part  upon  local  chemical  conditions  and  upon 
the  amount  of  the  blood-pressure.  When  we  shall  dis- 
cuss the  physiologic  features  of  emotion  we  shall  emphasize 
the  value  to  the  muscles  of  the  internal  secretion  known 
as  adrenalin.  This  is  poured  out  by  the  adrenal  bodies 
in  times  of  excitement  and  has  a  marked  effect  in  the 
direction  of  reinforcing  contraction  and  postponing  fatigue. 
To  adrenalin  we  may  ascribe  a  share  in  conferring  upon 
the  individual  what  we  recognize  as  the  "strength  of 
desperation."  Such  a  chemical  adjustment  may  occur 
in  delirium  or  under  hypnosis. 

In  the  last-named  condition  it  is  a  common  demon- 
stration to  extend  the  body  of  the  subject  from  one  chair 
to  another  and  to  seat  another  person  upon  him  midway 
between  the  points  of  support.  The  muscles  which  suc- 
cessfully meet  this  severe  test  may  be  untrained  and 
insignificant  in  appearance.  Is  their  unexpected  rigidity 
due  to  chemical  alterations  in  their  make-up  or  to  a 
stimulation  of  their  fibers  which  is  much  more  inclusive 
than  can  ordinarily  be  secured?  May  not  both  classes 
of  factors  be  present  at  once? 


THE    NEUROMUSCULAR   MECHANISM  93 

We  need  not  refer  to  unusual  or  pathologic  examples  to 
confirm  the  nnpression  that  the  degree  of  command  ex- 
erted by  the  nervous  system  varies  very  widely  indeed. 
The  most  energetic  responses  are  probably  those  produced 
when  a  number  of  afferent  channels  are  simultaneously 
used  to  promote  movements  which  could  be  reflexly 
evoked  in  connection  with  either  one  of  these  paths. 
Camis^  has  shown  that  in  the  lower  animals  it  is  possible 
to  secure  more  powerful  reflex  contractions  by  stimulating 
two  sensory  nerves  at  once  than  can  be  caused  to  occur  by 
the  most  intense  excitation  of  either  of  these  paths  by 
itself.  Some  would  interpret  this  result  to  mean  that  the 
same  perikarya  are  more  strongly  stimulated  when  the 
approach  is  made  through  the  larger  number  of  afferent 
fibers;  others  would  infer  that  a  larger  number  of  motor 
neurons  are  made  accessible  to  the  influence  of  the  stimu- 
lation. Possibilities  hke  these  will  receive  additional  dis- 
cussion when  we  reach  the  subject  of  fatigue  and  its 
postponement. 

Coordination. — This  word  has  already  been  said  to  be 
so  comprehensive  that  it  can  be  made  to  express  the  main 
function  of  the  entire  nervous  system.  It  must  now  be 
viewed  with  especial  reference  to  the  execution  of  muscular 
movements.  We  seldom  call  into  voluntary  action  a 
single  muscle  quite  unaffected  by  any  other.  The  use  of 
solitary  muscles  in  pure  reflexes  is  equally  rare.  In  the 
vast  majority  of  cases,  though  we  may  be  able  to  select 
one  muscle  as  the  chief  performer,  we  have  to  recognize 
the  auxiHary  part  played  by  its  fellows  in  carrying  out 
even  what  seems  a  simple  movement.  It  is  theoretically 
possible  to  bend  the  elbow  by  contracting  a  single  muscle, 
the  biceps  humeri,  but  in  executing  the  act  in  the  habitual 
manner  we  find  that  the  other  muscles  of  the  arm  are  not 
passive,  but  are  changing  their  tension  in  such  a  way  as  to 
give  steadiness,  precision,  and  economy  of  force  to  the 
whole  proceeding.  Certain  ones  directly  reinforce  the 
essential  movement,  others  assist  indirectly  by  making 
1  Journal  of  Physiology,  1909,  xxxix,  228. 


94  •    THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

more  stable  the  parts  of  the  skeleton  which  must  be  held 
as  a  fixed  anchorat^e  with  relation  to  the  parts  in  motion. 

Particular  attention  must  be  directed  to  the  inhibitory 
phenomena  which  are  known  to  accompany  most  move- 
ments. Sherrington,  of  Liverpool,  holds  the  foremost 
place  among  those  whose  researches  have  served  to  reveal 
the  importance  of  this  matter.  When  a  muscle  is  selected 
at  random  and  its  mechanical  relations  are  observed,  we 
can  usually  find  one  or  more  other  muscles  which  can  be 
recognized  as  adapted  to  pull  against  it.  We  say  that 
these  muscles  are  the  antagonists  of  the  first.  So  in  the 
case  of  the  biceps  humeri,  already  mentioned  as  applying 
its  force  to  raise  the  forearm  and  to  bend  the  elbow,  we 
see  that  the  triceps,  on  the  back  of  the  upper  arm,  must 
have  the  opposite  effect.  Technically  speaking,  the  biceps 
is  a  flexor  and  the  triceps  an  extensor. 

In  other  parts  of  the  body  we  find  muscles  which  are 
less  clearly  arranged  to  act  as  antagonists,  but  the  prin- 
ciple is,  notwithstanding,  a  general  one.  Certain  muscles 
raise,  while  others  depress,  the  ribs.  The  analysis  of  such 
effects  becomes  more  difficult  when  we  consider  examples 
like  the  bending  and  straightening  of  the  back  in  which 
many  muscles  participate.  The  diaphragm  offers  a  curious 
illustration;  when  its  center  is  drawn  downward  by  the 
contraction  of  its  marginal  portions  the  viscera  are 
crowded  aside  and  must  be  accommodated  by  the  stretch- 
ing of  the  muscular  abdominal  walls.  Hence,  the  ab- 
dominal muscles  are  collectively  antagonists  of  the  dia- 
phragm, but  the  transmission  of  pressure  is  through  the 
contents  of  the  cavity.  Sometimes  opposing  muscles 
are  of  very  unequal  strength.  It  is  plain  that  those 
which  raise  the  lower  jaw  and  set  the  teeth  are  incom- 
parably more  powerful  than  those  which  make  the  counter- 
movement,  and  there  is  little  occasion  for  a  strong  mechan- 
ism in  the  second  case. 

Often  we  contract  antagonistic  muscles  simultaneously 
and  with  balanced  force.  This  is  done  when  the  object  is 
to  secure  firmness  in  any  part — to  resist  the  tendency  to 


THE    NEUROMUSCULAR    MECHANISM  95 

move  rather  than  to  cause  a  movement.  When  a  hmb 
which  was  previously  held  firm  by  such  means  is  suddenly 
bent,  it  can  be  shown  that  two  changes  have  occurred. 
Not  only  have  the  flexors  shortened,  but  their  opponents, 
the  extensors,  have  been  inhibited.  They  do  not  actually 
push,  but  they  cease,  in  a  perfectly  definite  way,  to  resist 
the  movement  which  is  to  be  brought  about.  Sherrington 
showed  this  in  the  most  convincing  manner  by  an  experi- 
ment in  which  the  rotation  of  the  eyeball  was  under  ob- 
servation. He  first  determined  conditions  under  which 
he  could  unfailingly  secure  the  turning  of  the  eye  in  a 
certain  direction,  we  will  say,  toward  the  nose.  The 
responsibility  would  seem  to  lie  with  the  internal  rectus 
muscle.  By  cutting  the  nerve  of  this  muscle  he  paralyzed 
it.  Then,  repeating  the  stimulation  which  had  caused  the 
reaction  before,  he  still  saw  the  eyeball  swinging  in  the 
old  direction,  though  not  so  far  as  before. 

What  happened,  that  the  eye  should  continue  to  turn 
as  though  drawn  by  a  muscle  now  disconnected  from  the 
nervous  system?  The  movement  could  be  explained  only 
upon  the  supposition  that  the  antagonistic  muscle  did  not 
fully  relax  until  the  action  of  its  governing  neurons  was 
suspended  at  a  moment  when  those  normally  presiding 
over  its  opponent  were  stimulated.  A  diagram  will  be 
helpful.  In  the  leg  of  an  animal  the  same  type  of  inhibi- 
tion has  been  demonstrated.  If  a  reflex  extension  has  been 
secured  so  frequently  as  to  be  predictable  and  a  flexor 
muscle  is  then  detached  from  the  joint,  but  left  in  connec- 
tion with  its  nerve,  this  muscle  will  be  found  to  lengthen 
whenever  the  reflex  is  executed.  It  is  the  "law  of  recipro- 
cal innervation"  that  when  the  centers  excite  a  set  of 
muscles  the  antagonists  are  inhibited.  By  inhibition 
in  this  case  is  meant  the  cessation  of  a  mild  continuous 
stimulation  which  is  normally  brought  to  bear  upon  all 
muscles  excepting  at  such  times  (Fig.  18). 

It  will  now  be  evident  that  a  coordinated  movement 
requires  the  excitation  of  some  muscles,  each  in  an  ap- 
propriate degree,  and  the  abolition  of  the  habitual  residue 


90-     THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

of  contraction  (tonus)  in  other  muscles,  which  must 
.vield  readily  that  they  may  not  hinder  the  movement. 
In  all  ])ut  the  simplest  instances  another  element  comes 
in,  that  of  sequence  or  succession  in  the  responses  of  indi- 
\ddual  nmscles.  Most  movements  occur  in  stages  and 
many  have  an  alternating  character.  When  this  is  true 
we  must  suppose  that  each  step  establishes  conditions  of 
pressure  or  tension  in  the  moving  parts  of  such  a  nature 
as  to  excite  certain  receptors,  and  that  the  next  shift  in 
the  musculature  follows  as  a  reflex.  In  the  higher  animals 
and  in  man  only  a  little  of  this  coordinating  power  resides 


Fig.  IS. — The  principle  of  reciprocal  innervation.  The  cortical 
neuron  is  represented  as  exciting  the  upper  of  the  two  subordinate 
neurons,  causing  the  contraction  of  one  group  of  muscle-fibers, 
while  it  inhibits  the  second  neuron,  allowing  the  associated  muscle- 
fibers  to  relax.  The  +  sign  suggests  stimulation;  the —  sign,  in- 
hibition.    Doubtless  the  actual  arrangement  is  less  simple  than  this. 


in  the  spinal  cord.  Most  of  it  is  represented  in  the  brain. 
At  this  place  it  is  convenient  to  speak  briefly  of  the 
physiology  of  the  cerebellum. 

The  Cerebellum. — It  will  be  recalled  that  this  division 
of  the  brain  is  a  dorsal  outgrowth  of  the  nerve-axis.  It  is 
connected  by  a  rich  supply  of  fibers  with  the  medulla 
behind,  the  ventral  region  known  as  the  pons,  and,  less 
directly,  with  the  cerebrum.  Its  prominence  in  different 
species  of  animals  is  most  unequal.  It  is  large  in  the  fish, 
greatly  reduced  in  the  frog,  very  large  again  in  the  bird, 
and  fairly  large  but  overshadowed  by  the  cerebrum  in 
most  mammals.     A  moment's  reflection  will  show  that  the 


THE  NEUROMUSCULAR  MECHANISM        97 

size  of  the  cerebellum  can  scarcely  be  correlated  with  the 
intelligence  of  these  types;  further  consideration  inclines 
one  to  the  belief  that  it  is  in  some  sense  linked  with 
elaborate  and  active  neuromuscular  mechanisms. 

A  fish  gives  little  indication  of  intelhgence,  but  it  has  a 
most  multifarious  muscular  system  corresponding  with 
its  intricately  developed  skeleton.  The  bird  has  much 
more  intelligence,  but  is  distinguished  most  clearly  by  its 
powers  of  flight.  A  prominent  cerebellum  seems  always  to 
imply  capacity  for  locomotion  and  balancing.  This  gen- 
eral contention  is  borne  out  by  the  results  of  experiments 
in  which  this  part  of  the  brain  has  been  partially  or  wholly 
removed.  When  a  physiologist  wishes  to  determine  the 
service  of  a  particular  structure  in  the  nervous  system 
he  cuts  it  away,  if  this  is  possible,  and  keeps  the  animal 
alive  to  observe  the  resulting  deficiency.  This  procedure 
is  justified  only  when  two  conditions  are  fufilled:  first, 
no  pathways  between  other  stations  than  that  under  ob- 
servation must  be  interrupted;  second,  the  effects  recorded 
must  be  those  due  to  the  actual  lack  of  the  part  which  has 
been  sacrificed,  and  not  to  the  irritation  set  up  at  the  seat 
of  the  operation. 

The  pioneer  experiments  upon  the  cerebellum  were 
made  in  France  about  one  hundred  years  ago.  The 
investigator  found  that  a  pigeon  recently  deprived  of  this 
part  of  the  brain  gave  a  distressing  picture  of  incoordina- 
tion. The  bird  could  not  fly  nor  even  keep  its  feet.  Its 
struggles  were  painful  to  witness,  and  the  more  so  because 
there  seemed  to  be  no  lessening  of  the  normal  sensitive- 
ness and  capacity  for  terror.  In  its  staggering  and  flut- 
tering about  there  was  no  apparent  loss  of  the  power  to 
contract  individual  muscles,  but  the  most  obvious  loss 
of  the  ability  to  secure  the  needful  cooperation  of  the 
groups  on  whose  action  equilibrium  in  rest  or  motion 
depends.  The  doctrine  based  on  such  observations  was 
to  the  effect  that  the  cerebellum  is  in  charge  of  the  general 
musculature  so  far  as  this  is  used  for  equilibration  and 
perhaps  for  other  habitual  types  of  performance. 

7 


98  '   THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

The  work  of  more  recent  students  has  sliown  that  the 
control  formerly  credited  to  the  cerebellum  was  too 
absolute  and  exclusive.  Our  belief  is  still  that  this 
part  of  the  brain  is  much  concerned  with  subconscious 
muscular  adjustments  requiring  extensive  coordination, 
but  we  no  longer  regard  it  as  the  sole  seat  of  such  regula- 
tion. It  has  been  found  that  animals  recover  in  great 
part  from  the  profound  effects  of  the  removal  of  the 
cerebellum,  and  it  is  natural  to  conclude  that  the  imme-. 
diate  results  which  are  so  striking  are  due  largely  to  irrita- 
tion at  the  place  operated  upon  and  not  so  definitely  to 
the  loss  of  its  functioning.  The  recovery  is  never  com- 
plete. A  dog  without  a  cerebellum  may  walk  and  swim 
again,  but  not  with  the  full  vigor  and  steacUness  of  the 
normal  animal.  Some  element  of  reinforcement  or  com- 
pensation is  permanently  lacking. 

As  regards  the  human  nervous  system,  it  is  usually  held 
that  the  cerebellum  is  developed  by  practice  and  that  it 
comes  to  contain  much  of  the  synaptic  machinery  for 
maintaining  the  balance  at  rest  and  in  motion.  It  has 
often  been  supposed  to  assume  command  of  complex 
movements  which  were  at  first  guided  at  all  stages  by 
the  cerebrum.  Thus,  it  has  been  imagined  that  a  child 
learning  to  walk,  whose  attention  is  plainly  concentrated 
upon  the  taking  of  each  step,  is  dictating  its  uncertain 
movements  from  the  cerebral  cortex,  but  that  the  higher 
mechanism  is  in  time  relieved  of  the  detail  and  set  free 
for  new  activities,  the  cerel^ellum  taking  its  place,  at  least 
to  a  considerable  extent. 

If  this  is  a  correct  conception,  it  may  be  inferred  that 
later  acquirements  of  the  individual,  such  as  swimming 
or  skating,  may  likewise  call  for  cerebral  direction  until 
they  become  easy  and  unconscious,  when  their  govern- 
ment may  be  cerebellar.  According  to  this  view,  the 
cerebellum  is  intimately  related  to  all  accomplishments 
which  we  can  speak  of  as  "second  nature."  But  this  is 
more  certainly  true  of  those  which  involve  a  large  share 
of  the  muscles  than  of  localized  actions.    The  use  of  a 


THE    NEUROMUSCULAR   MECHANISM  99 

pen  probably  remains  essentially  a  cerebral  act,  though 
one  may  trace  a  copy  with  a  minimum  of  conscious 
attention.  Disease  of  the  cerebellum  interferes  chiefly 
with  movements  which  call  for  the  poising  and  timely 
control  of  the  main  mass  of  the  body  rather  than  with 
skill  of  hand. 

Students  are  slow  to  realize  the  vast  importance  of 
afferent  impulses  in  the  execution  of  coordinated  move- 
ments. When  one  sees  a  victim  of  spinal  disease  whose 
disorderly  and  badly  regulated  motions  make  him  a 
painful  spectacle,  it  is  natural  to  infer  that  there  is  inabil- 
ity to  command  the  muscles.  Yet  if  it  is  a  case  of  typic 
locomotor  ataxia  the  chief  trouble  is  with  the  ascending 
paths.  The  afflicted  man  suffers  from  the  want  of  a  guid- 
ing sense.  He  cannot  readily  perceive  the  extent  of  the 
movements  which  he  is  executing,  nor  the  resistances 
encountered.  He  is  likely  to  do  much  better  when  he 
has  the  use  of  his  eyes  than  he  can  in  the  dark.  All  people 
are  assisted  by  the  eyes  in  the  maintenance  of  equilib- 
rium, but  these  receptors  become  still  more  important 
when  there  is  a  failure  of  the  impulses  from  the  motor 
apparatus  itself. 

Breathing. — An  important  subdivision  of  the  general 
neuromuscular  system  is  that  which  stands  in  control  of 
breathing.  The  muscles  used  are  such  as  we  can  employ 
singly  or  in  groups  for  various  purposes.  We  can  also 
modify  our  breathing  if  we  choose,  but  only  within  limits. 
It  is  supposed  to  be  impossible  to  commit  suicide  by 
holding  the  breath.  It  is  increasingly  difficult  to  continue 
forcing  the  breathing  beyond  one's  inclination.  Since 
we  cannot  long  underbreathe,  nor  yet  overbreathe,  it  is 
natural  to  assume  that  there  is  some  positively  acting, 
involuntary  mechanism  normally  dictating  the  rate  and 
depth  of  the  breathing  movements.  We  have  evidence 
of  very  long  standing  that  this  mechanism  indeed  exists 
and  that  its  chief  center  is  in  the  medulla. 

Breathing  is  not  dependent  upon  the  cerebral  cortex. 
Complete  division  of  the  nervous  axis  at  the  level  of  the 


100"     THE    NERVOUS   SYSTEM    AND    ITS   CONSERVATION 

pons  docs  not  stop  the  respiration.  If  the  injury  is  cx- 
tondcd  l)a{'kward  into  the  nieckiUa,  breathing  is  susi)ondcd 
permanently  when  certain  cell-chisters  are  destroyed  or 
when  they  are  cut  off  from  communication  with  the 
spinal  cord.  The  French  workers  who  first  demonstrated 
the  absolute  dc^pendence  of  life  upon  the  integrity  of 
this  very  limitetl  region  called  it  the  "vital  knot."  It  is 
generally  referred  to  as  the  respiratory  center.  It  is  so 
related  to  the  remainder  of  the  nervous  system  that  it  is 
involved  in  almost  every  reflex  act  of  any  magnitude. 
Its  ordinary  action  seems  to  be  determined  by  the  condi- 
tion of  the  blood  which  is  sent  to  it.  If  the  dissolved 
carbon  dioxid  is  increased,  the  center  is  excited  to  cause 
deeper  and  quicker  breathing.  If  the  same  gas  is  reduced 
to  an  unusualh^  low  concentration  in  the  blood,  the  stimu- 
lation of  the  center  is  suspended  and  there  is  a  pause  in 
the  breathing  (apnea). 


CHAPTER  VIII 

THE    NEUROMUSCULAR    SYSTEM:     NEUROMUS- 
CULAR FATIGUE 

Nothing  is  more  familiar  than  the  fact  of  experience 
that  muscles  used  long  and  severely  respond  less  and  less 
readily  to  our  requisitions  upon  them.  This  progressive 
flagging  of  efficiency,  together  with  the  subjective  sense  of 
difficulty  in  commanding  the  muscles  employed,  we  speak 
of  as  fatigue.  When  we  add  the  adjective  "neuromuscu- 
lar" we  open  the  way  to  a  discussion  of  the  respective 
share  of  muscular  and  nervous  elements  in  the  develop- 
ment of  this  condition.  In  the  laboratory  we  can  devise 
experiments  such  that  fatigue  of  muscle  is  studied  quite 
by  itself;  in  the  living  body  muscles  are  used  only  when 
their  controlling  nervous  mechanisms  are  in  action. 

Fatigue,  whether  in  muscular  fibers  or  in  neurons,  may 
conceivably  result  from  either  of  two  causes.  It  will  be 
inevitable  if  the  store  of  energy-producing  substance 
runs  low.  This  is  a  type  of  fatigue  which  approaches  ex- 
haustion as  a  limit.  The  second  possibility  is  that  by- 
products or  end-products  of  the  chemical  process  which 
is  going  on  may  so  accumulate  as  to  become  a  hindrance 
to  the  continuance  of  that  process.  This  is  probably  the 
ordinary  happening:  muscles  which  refuse  to  work  are 
not  destitute  of  all  fuel,  but  are,  figuratively  speaking, 
clogged  by  ashes  and  half-burned  clinkers  which  remain 
as  relics  of  the  combustion  which  has  recently  taken 
place. 

So  far  as  muscular  tissue  is  concerned,  we  know  some- 
thing of  the  products  which  are  capable  of  depressing  its 
activity.  Three  compounds  are  usually  mentioned  as 
bearing    a    part — carbon    dioxid,    lactic    acid,    and    acid 

101 


102  "    THE    NERVOUS    SYSTEM    AND    ITS   CONSERVATION 

potassium  phosphate.  These  are  all  acidic  in  nature,  and 
it  is  supposed  that  any  other  acid,  introduced  experi- 
mentally, will  have  a  similar  effect.  Undefined  fatigue 
substances  probably  exist  in  addition  to  the  ones  named, 
and  they  may  not  all  have  an  acid  character.  A  most 
important  fact  to  be  noted  with  regard  to  these  metabolic 
products  is  this:  the  same 'compounds  which  in  high  con- 
centration can  poison  the  muscle  to-  the  point  of  apparent 
paralysis,  act  as  stimulants  when  they  are  present  in  small 
amounts.  In  this  we  find  one  explanation  of  the  favorable 
effect  of  moderate  preliminary  exercise  upon  muscular 
capacity.  A  muscle  is  not  so  efficient  when  it  is  first 
aroused  to  activity  after  a  period  of  rest  as  it  is  when  it 
has  been  used  for  a  time.^ 

The  phenomenon  referred  to — the  gain  in  power  which 
comes  with  a  brief  series  of  contractions — is  spoken  of  as 
the  "stair-case  effect,"  or  often,  using  a  German  equivalent, 
as  the  Treppe.  The  proof  that  it  is  due  in  part  at  least  to 
the  so-called  fatigue  substances  we  owe  to  Lee  of  Colum- 
bia. Other  factors  undoubtedly  enter  in;  when  one  is 
"warming  up"  one  profits  by  the  adaptation  of  the  cir- 
culatory system  to  the  new  requirements  and,  perhaps, 
also  by  changes  in  the  activity  of  the  organs  of  internal 
secretion.  But  when  all  allowance  has  been  made  for 
such  sources  of  reinforcement,  we  must  still  attribute 
much  to  the  favorable  influence  of  the  products  of  activ- 
ity exerted  before  their  accumulation  has  become  excessive. 

We  are  now  in  position  to  consider  the  probable  seat  of 
fatigue  in  the  neuromuscular  apparatus.  Recalling  the 
unit  of  this  mechanism  as  previously  defined,  we  find 
that  the  possibilities  are  more  numerous  than  would  at 
first  be  supposed.  The  muscle-fiber  may  be  fatigued. 
The  junction  of  nerve  and  muscle,  the  motor  end-plate, 
is  another  structure  which  is  subject  to  impairment  by 
its  own  use.  This  is,  indeed,  a  relatively  weak  hnk  in 
the  chain.  Fatigue  of  the  nerve-fiber  may  be  disregarded; 
the  enduring  nature  of  the  white  matter  has  already  been 
1  F.  S.  Lee,  Pop.  Sci.  Monthly,  February,  1910. 


THE    NEUROMUSCULAR   SYSTEM;   FATIGUE  103 

commented  upon  (see  page  39).  But  fatigue  of  the 
motor  perikaryon  is  to  be  reckoned  with,  and  so  is  fatigue 
at  the  synapses  through  which  its  discharges  are  deter- 
mined. It  is  not  wise  to  make  dogmatic  assertions  as  to 
the  precise  order  in  which  failure  of  these  unlike  struc- 
tures is  to  be  anticipated  when  they  are  kept  steadily  at 
work. 

If  a  proper  balance  between  destructive  and  recupera- 
tive processes  can  be  struck,  a  neuromuscular  mechanism 
need  not  exhibit  fatigue  in  spite  of  what  seems  like  con- 
tinuous use.  This  is  the  case  with  the  diaphragm,  which 
bears  its  part  in  the  taking  of  every  breath,  but  seems  not 
to  show  any  weakening  of  response  or  loss  of  irritability 
until  it  shares  the  general  decline  of  old  age.  As  the 
diaphragm  is  not  automatic,  but  contracts  only  in  response 
to  stimulation  traceable  to  the  brain,  we  must  suppose 
that  in  the  nervous  as  well  as  in  the  muscular  portions  of 
this  combination  restoration  normally  keeps  pace  with 
decomposition,  and  that  the  waste-products  are  not  suf- 
fered to  gather  at  the  seat  of  action.  (The  diaphragm 
is  chosen  rather  than  the  heart  to  exemplify  this  balance 
because  the  beating  of  the  heart  is  not  dictated  from 
without.) 

If  we  leave  out  of  further  account  the  muscles  used  in 
breathing  and  their  presiding  neurons,  we  shall  be  ready 
to  agree  that  in  general  our  neuromuscular  equipment  is 
subject  to  daily  if  not  more  frequent  fatigue,  and  calls  for 
rest  that  it  may  be  renewed.  The  renewal  must  include 
the  washing  away  or  perfect  neutralization  of  the  fatigue 
substances  and  the  introduction  of  fresh  fuel  supplies. 
To  make  our  discussion  concrete,  let  us  fix  our  attention 
upon  an  imaginary  pedestrian  who  is  found  toward  the  end 
of  the  day  covering  the  last  mile  of  a  long  tramp.  In  what 
respects  is  his  system  altered  from  its  state  at  setting  out 
in  the  morning? 

His  leg  muscles  have  done  the  heaviest  work.  They  have 
produced  in  the  course  of  the  walk  a  great  quantity  of 
carbon  dioxid.    This  has,  presumably,  been  removed  quite 


104  ■    THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

promptly  and  full>-  through  the  lungs.  But  the  other  acid 
products  may  now  be  present  to  an  extent  which  suffices  to 
render  the  musck's  less  responsive  to  central  command.  The 
same  or  similar  compounds  may  have  affected  the  motor 
end-plates  in  such  a  way  as  to  make  difficult  the  trans- 
mission of  effects  from  nerve  to  muscle.  If  a  blockade  is 
established  at  this  point,  muscular  response  may  fail  at  a 
time  when  there  is  yet  plenty  of  potential  working  capac- 
ity in  the  muscles  themselves.  It  is  generally  held  that 
this  is  just  what  occurs:  the  end-plates  become  imper- 
vious to  stimuli,  while  other  parts  of  the  apparatus  are 
still  in  fair  working  order. 

One  is  tempted  to  draw  a  comparison  between  the  end- 
plate  and  a  safety-fuse,  such  as  is  used  in  connection  with 
an  electric  fixture.  The  fuse  is  intended  to  be  destroyed 
under  conditions  which  might  otherwise  threaten  damage 
to  more  valuable  portions  of  the  system.  It  is  readily 
renewed.  So  we  may  think  of  the  end-plate  as  some- 
thing easily  impaired  by  use,  but  also  easy  to  repair.  It 
is  better  that  wear  and  tear  should  fall  upon  this  structure 
rather  than  upon  the  more  highly  organized  protoplasm 
of  nerve-cells  or  muscle-fibers.  We  may  now  assign  as 
one  condition  associated  with  our  walker's  painful  prog- 
ress the  increasing  difficulty  of  end-plate  transmission. 

Another  condition  is  operative  at  the  same  time.  This 
is  the  persistent  return  from  the  musculature  itself,  the 
joints,  and  the  soles  of  the  feet  of  afferent  impulses  in- 
hibitory to  continued  walking.  In  part  these  impulses 
give  rise  to  sensations  of  lameness  and  weariness.  In 
part  they  may  impede  action  without  having  their  sign 
manifest  in  consciousness.  Fatigue,  so  far  as  it  is  due 
to  impulses  of  this  class,  may  be  regarded  as  disinclination 
rather  than  incapacity.  If  we  are  ingenuous  we  must 
admit  that  much  of  our  fatigue  has  to  be  classified  under 
this  head.  Such  a  source  of  deterrent  impulses  as  a  blis- 
tered foot  has  a  double  effect  upon  the  sufferer.  Besides 
making  him  feel  disposed  to  stop,  it  causes  him  to  adopt 
an  unnatural  gait  in  the  endeavor  to  "favor"  the  injured 


THE    NEUROMUSCULAR    SYSTEM:    FATIGUE  105 

member,  and  this  means  that  comparatively  untrained 
muscles  are  called  upon.  Endurance  is  thus  inevitably 
lessened. 

We  have  now  recognized  two  probable  elements  in  the 
famihar  state  of  the  tired  man.  These  are  end-plate  fatigue 
and  inhibitory  impulses  mounting  to  the  centers.  Addi- 
tional factors  are  undoubtedly  concerned.  Among  these 
we  may  include  some  measure  of  true  muscular  fatigue, 
dependent  on  the  local  chemical  changes  in  the  contractile 
material  and  perhaps  on  changes  in  the  composition  of  the 
blood  and  lymph.  We  must  bear  in  mind  that  fatigue 
substances  of  this  class  may  be  distributed  far  and  wide 
by  the  circulation  and  depress  the  functional  activity  of 
muscles  which  have  not  themselves  been  much  used.  An 
unfavorable  effect  spreading  to  glands  and  to  the  nerve- 
centers  is  easily  possible.  Our  pedestrian  may  be  feehng 
the  results  of  such  a  diffuse  poisoning  as  he  plods  along. 

Deterioration  of  the  motor  perikarya  in  the  cord  and 
perhaps  in  the  brain  may  be  one  source  of  the  observed 
waning  of  power.  Reference  has  been  made  some  time 
since  to  the  demonstration  of  visible  changes  in  these 
bodies  which  Hodge  and  others  have  succeeded  in  making 
conclusive.  A  new  picture  of  the  central  element  in  general 
fatigue  we  owe  to  the  school  of  Sherrington,  and  particu- 
larly to  one  recently  associated  with  him,  Alexander 
Forbes.^  This  new  emphasis  is  placed  upon  the  synapses 
through  which  stimulation  of  the  motor  perikarya  must 
be  accomplished.  Each  typic  perikaryon  has  a  number 
of  these  possible  approaches.  When  it  takes  part  in  a 
simple  reflex  it  is  not  excited  through  the  same  synapse  as 
though  the  stimulation  were  conveyed  to  it  from  the 
brain. 

Now,  there  is  reason  to  believe  that  synapses,  like  end- 
plates,  are  links  of  limited  endurance  in  the  neuromuscular 
chain.  If,  however,  a  synapse  becomes  fatigued  and  in- 
capable of  efficient  conduction,  there  is  the  possibility, 
not  present  in  the  case  of  the  end-plate,  of  substituting  a 
1  American  Journal  of  Physiology,  1912,  xxxi,  102. 


1U(J      THE    \p]RVOUS    SYSTEM    AND  'ITS    CONSERVATION 

new  route  for  the  application  of  stimuli.  We  have  very 
satisfactory  evidence  that  some  of  these  synapses  do  fa- 
tigue, and  that  an  apparent  renewal  of  motor  connnand 
is  secured  when  new  ways  of  stinuilation,  involving  differ- 
ent sensory  paths,  are  devised.  Let  us  suppose  that  our 
weary  traveler  suddenly  hears  martial  music.  If  it  is  his 
nature  to  be  moved  by  the  strains  we  may  expect  that, 
for  a  time,  his  pace  will  be  ciuickened  and  all  external 
signs  of  fatigue  diminished. 

How  shall  we  interpret  the  marked  effect  of  the  music? 
There  may  be  more  than  one  opinion  as  to  this,  but  we 


Fig.  19. — The  principle  of  fatigue  in  reflex  action — Forbes' 
conception.  When  the  reflex  obtained  through  r  fails,  the  action 
can  be  renewed  by  shifting  stimulation  to  ri.  The  motor  parts 
are  the  same  in  both  cases,  hence  the  fatigue  is  in  a  route  of  approach 
to  the  center.  One  must,  in  imagination,  multiply  all  the  elements 
illustrated.  ^ 


may  indicate  a  possible  explanation  along  the  lines  of 
Forbes'  experiments.  First,  we  must  briefly  describe  his 
methods.  He  has  studied  the  fatigue  of  the  reflex  mech- 
anism in  cats.  A  nerve  containing  afferent  fibers  is  chosen 
and  its  central  end  is  stimulated.  Certain  muscles  re- 
spond, and  one  of  these  is  selected  for  careful  observation. 
When  the  stimulation  is  applied  repeatedly  the  contrac- 
tions of  the  muscle  are  progressively  reduced  until  at 
length  none  can  be  secured.  Fatigue  at  some  point  in  the 
apparatus  is  to  be  inferred,  but  where?  The  answer  is 
forthcoming  when  a  shift  of  the  electrodes  is  made  to 


THE    NEUROMUSCULAR   SYSTEM:    FATIGUE  107 

another  afferent  nerve.  Such  a  shift  is  followed  by 
renewed  activity  on  the  part  of  the  muscle  to  which 
attention  is  directed  (Fig.  19). 

In  this  case  the  motor  elements  used  in  the  earlier  and 
in  the  later  part  of  the  trial  are  presumably  the  same. 
It  is  the  afferent  neurons  which  are  different.  Fatigue  of 
nerve-fibers  is  negligible,  and  the  conclusion  must  be  that 
failure  to  conduct  has  occurred  at  the  place  where  the 
impulses  of  peripheral  origin  must  exert  their  effect  upon 
the  motor  neurons.  This  is  the  same  as  saying  that  we 
have  here  an  instance  of  synaptic  fatigue.  Much  poten- 
tial capacity  for  action  may  still  reside  in  the  efferent 
equipment,  but  a  new  line  of  approach  must  be  adopted 
to  demonstrate  it.  Forbes  has  used  animals  in  which  only 
the  cord  and  not  the  brain  has  been  intact,  thus  simplify- 
ing his  conditions  as  far  as  he  could.  It  seems  legitimate 
to  extend  the  same  principle  to  muscular  performances  in 
which  the  brain  is  concerned.  This  we  shall  now  under- 
take to  do. 

The  neurons,  which  have  their  perikarya  in  the  cortex 
of  the  cerebrum  and  send  their  dependent  projection 
fibers  down  the  spinal  axis,  are  not  self -stimulated.  They 
are  thrown  into  action,  like  the  neurons  of  lower  rank, 
by  impulses  affecting  them  through  synapses.  Now  we 
may  fairly  suppose  that  the  efficiency  of  these  cerebral 
motor  neurons  is  greatest  when  they  are  stimulated  from 
all  sides,  so  to  speak,  rather  than  in  a  one-sided  fashion. 
Here  we  have  a  key  to  the  invigorating  influence  of 
rhythmic  music  upon  the  walker  and  perhaps  to  many 
other  phenomena  of  the  same  class. 

The  tired  man  to  whom  we  have  so  often  referred  has 
been  kept  in  motion  through  the  day  by  a  variety  of 
external  stimuli.  Some  of  these  have  had  a  very  direct 
effect  upon  the  lower  centers,  as  in  the  case  of  the  im- 
pulses returning  from  the  soles  of  the  feet  at  every  con- 
tact with  the  ground.  These,  together  with  others  from 
the  joints,  the  tightening  tendons,  and  probably  from 
the  muscles  themselves,  have  been  ever  prompting  the 


108      THE    NEKVOUS    SYSTEM    AND    ITS    CONSERVATION 

taking  of  an  additional  step  to  Ijc  added  to  the  lengthening 
series.  Visual  impulses,  varied  with  the  ehanging  scenery, 
have  been  giving  rise  to  cerebral  currents  which  have 
favored  the  holding  of  the  muscles  to  their  long  task.  But 
now  a  time  has  come  when  the  impulses  returning  from  the 
locomotor  organs  are  deterrent  rather  than  encouraging. 
Inhibition  at  the  lower  centers  is  overridden  with  increas- 
ing difficulty  by  the  action  of  the  higher  comj^lexes. 

In  the  brain  itself  the  visual  currents  may  cease  to  be 
favorable.    There  is  no  longer  the  desire  to  see  bej^ond  the 

Impulses  Impulses   oj 

over  associatioTT'^"^^       ^  _^  ^^-—^  Visual  orj^l  17 

patl)S.  "Will."  X^  "^^ 

/Ctrchral    \ 


)r 


rv 


Deterrent 

Impu-lses 


y 


[      Afo(o) 
V  Centre,  /'  "^^-^  Impulses  of 


-  Motor 
iropuises 


auditory  ori^i'?' 


Fig.  20. — To  suggest,  though  incompletely,  the  concentration  of 
certain  streams  of  impulses  upon  the  motor  cortex  in  one  tired  by 
prolonged  exertion.  To  bring  in  play  a  fresh  path  of  approach  is  to 
secure  some  renewal  of  activitj\  To  abate  the  deterrent  impulses 
has  a  like  efTect. 

next  turn  of  the  road  or  to  gain  the  next  ridge.  What  is 
needed  to  rouse  the  flagging  cortical  centers  is  stimula- 
tion over  afferent  paths  that  have  not  yet  been  brought 
into  use.  One  of  these  is  the  auditory  nerve.  The  ear 
has  had  but  Httle  to  do  with  reinforcing  the  walker's 
efforts  up  to  this  time.  Hence  the  music  wakes  to  ready 
response  a  part  of  the  nervous  system  which  has  been 
but  little  fatigued  by  any  action  strictly  its  own,  although 
the  overflow  of  fatigue  substances  formed  elsewhere  may 
have  injured  it  to  some  extent.  The  cortical  motor 
neurons  are  reached  over  paths  nearly  inactive  until  now 


THE    NEUROMUSCULAR    SYSTEM:    FATIGUE  109 

and  by  means  of  synapses  which  have  not  been  fatigued. 
The  new  application  would  be  vain  if  there  were  not  still 
muscular  resources  available  and  possil^ilities  of  synaptic 
transmission  from  the  projection  fibers  of  the  cerebrum  to 
the  motor  neurons  of  the  cord  (Fig.  20). 

What  shall  we  say  of  the  soldier  who  is  roused  from 
what  seemed  to  be  utter  fatigue  by  the  close  pursuit  of 
the  enemy  and  the  whistle  of  bullets?  Is  this  a  simple 
case  of  setting  up  brain  currents  which  arrive  at  the 
motor  centers  by  fresh  routes  and  unimpaired  synapses? 
It  may  be  so  in  part,  but  whenever  a  strong  emotional 
reaction  is  entailed  there  are  likely  to  be  chemical  rein- 
forcements of  muscular  capability.  This  is  a  matter  which 
may  well  be  left  for  discussion  in  another  connection. 
The  general  principle  has  been  stated  in  the  last  chapter 
(see  page  92),  where  the  augmented  production  of  adren- 
alin in  times  of  excitement  was  mentioned. 

The  remarkable  postponement  of  fatigue  in  the  case 
of  those  who  like  to  dance  is  worthy  of  some  comment. 
Consider  the  country  girl,  whose  daily  tasks  are  heavy 
enough  to  leave  her  quite  tired  at  nightfall  and  ready  for 
an  early  bedtime.  On  the  exceptional  evening  when  there 
is  to  be  a  party  the  usual  day's  work  may  have  been  faith- 
fully done,  but  there  may  be  no  signs  of  the  accustomed 
weariness.  Instead,  she  goes  to  the  dance  and  for  hours 
pursues  a  form  of  vigorous  exercise  in  which  the  muscles 
used  are,  in  the  main,  the  same  which  were  called  upon 
in  the  domestic  round.  Perhaps  the  emotional  state  is 
intense  enough  to  warrant  the  belief  that  internal  secre- 
tions are  modified  to  support  the  muscular  activity. 
Whether  this  is  so  or  not,  we  can  see  that  the  conditions 
favor  an  extensive  and  symmetric  stimulation  of  the 
cortical  areas. 

When  the  girl  in  question  was  engaged  in  sweeping  a 
room  she  was  held  to  her  dull  duty  by  certain  internal 
stimuli  of  an  obscure  but  evidently  monotonous  char- 
acter. The  "sense  of  duty"  as  reahzed  in  consciousness  is 
attended  by  the  transmission  of  impulses  to  the  motor 


110      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

apparatus,  but  the  number  of  these  impulses  is  far  less 
than  it  might  be  if  various  external  conditions  favoring 
reinforcement  could  be  added.  At  the  dance  the  reinforc- 
ing factors  are  present  in  the  most  efficient  combination. 
Tlicre  is  the  music,  there  are  the  lights  and  the  shifting 
play  of  colors  as  the  figures  move,  there  are  contacts,  and 
all  the  while  a  richness  in  the  psychic  experience  totally 
foreign  to  the  drudgery  at  home.  This  psychic  richness 
doubtless  corresponds  with  the  physiologic  fact  of  multi- 
phed  brain-currents. 

The  difference  between  play  and  work,  between  doing 
what  we  keenly  enjoy  and  what  we  feel  we  ought  to  do  for 
some  remote  result,  may  be  said  to  be  the  difference  be- 
tween a  motor  performance  in  which  many  pathways  are 
traversed  by  the  impulses  which  unite  to  stimulate  the 
neuromuscular  mechanism  and  one  in  which  the  number 
of  these  paths  is  small  and  not  much  subject  to  variation. 
Titchener  once  surprised  an  audience  by  the  declaration 
that  "all  work  is  a  waste  of  time";  this  he  elucidated  as 
meaning  that  the  zest  which  we  associate  with  play  is  the 
basis  of  better  accomphshments  than  can  be  attained  when 
only  the  feeling  of  oliligation  is  operative.  The  boy  who 
becomes  very  tired  of  chopping  wood  can  use  the  same 
muscles  in  a  game,  and  his  parents  may  twit  him  with  the 
fact.  But  while  it  is  true  that  he  is  using  the  same  muscles 
and  the  same  spinal  neurons,  perhaps  the.  same  projection 
fibers  from  the  cerebrum,  he  is  not  using  the  same  afferent 
channels  nor  the  same  cortical  approaches  to  the  motor 
centers.  The  adult  cannot  honestly  lay  claim  to  im- 
munity from  fatigue  of  this  sort. 

Elements  in  Training. — A  great  deal  that  has  been  said 
in  this  and  the  preceding  chapter  may  conveniently  be 
reviewed  under  this  head.  In  what  respects  does  an  un- 
trained neuromuscular  system  differ  from  one  which  has 
been  developed  by  use?  We  shall  find  as  many  possibili- 
ties in  this  connection  as  we  have  in  our  attempt  to 
analyze  fatigue.  We  shall  have  to  pay  attention  to  the 
muscles,  the  end-plates,  and  the  central  organization. 


THE    NEUROMUSCULAR    SYSTEM:    FATIGUE  111 

One  fact  is  impressed  upon  the  mind  of  the  man  in  the 
street:  that  muscles  grow  with  use.  We  shall  not  be  in- 
clined to  make  this  the  foremost  consideration,  but  it  is 
well  worth  emphasizing.  This  is  not  the  place  to  enter 
upon  any  discussion  of  the  causes  underlying  this  well- 
known  growth.  It  may  be  due  in  part  to  improved  cir- 
culation and  in  part  to  chemical  conditions  arising  when 
contractions  take  place.  It  may  be  said  to  be  a  principle 
of  rather  wide  appUcation  in  biology  that  a  destructive 
process,  during  vigorous  life,  will  be  followed  not  only  by  a 
process  of  repair,  but  by  overcompensation.  This  is  held 
to  be  true  of  antitoxin  production  and  acquired  im- 
munity to  disease.  It  is  simply  illustrated  in  callous  for- 
mation: when  friction  destroys  the  surface  layers  of  the 
skin  they  are  not  merely  replaced,  but  their  number  is  in- 
creased. The  increase  in  the  mass  of  a  muscle  consequent 
on  its  regular  use  is  also  a  reaction  from  a  decomposition 
process,  for  every  contraction  is  executed  at  the  cost  of 
some  substance  disintegrated.  But  the  growth  of  the 
muscle  is  not  wholly  analogous  to  the  formation  of  a 
callus,  because  in  the  first  case  it  is  beheved  that  we  have 
no  multiphcation  of  fibers,  but  only  an  increase  in  volume 
on  the  part  of  those  present. 

One  may  make  proper  allowance  for  the  greater  size  of 
trained,  as  compared  with  untrained,  muscles,  and  he  will 
be  convinced  that  the  gain  in  power  is  out  of  all  proportion 
to  the  gain  in  bulk.  Betterment  of  quality  must  certainly 
be  admitted.  The  service  of  exercise  to  a  man  may  be 
rather  to  give  him  full  command  of  the  tissue  which  he  has 
than  to  put  more  at  his  disposal.  Superior  quality  in 
muscle  may  mean  an  actual  chemical  change  by  which  the 
fuel  is  made  more  available  or  stored  in  larger  quantity, 
or  the  chief  improvement  may  be  in  the  efficiency  of  the 
circulation.  Much  will  depend  upon  this,  for  the  supply 
of  oxygen  to  the  muscle  protoplasm  is  an  imperative 
requirement. 

In  the  third  place,  it  is  conceivable  that  facility  of 
end-plate  transmission  is  one  of  the  gains.    Difficulty  in 


112      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

securing  responses  because  of  conditions  existing  at  the 
junction  of  nerve  and  muscle  may  l)e  one  of  the  charac- 
teristics of  the  untrained,  as  it  is  of  the  fatigued,  state. 
The  increased  endurance  demonstrated  by  those  who  have 
put  themselves  upon  sparing  diets  (Fletcher,  Chittenden, 
et  al.)  is  most  easily  explained  on  the  theory  that  the 
end-plates  were  previously  subject  to  a  chronic  impair- 
ment owing  to  the  presence  of  avoidable  metabolic  prod- 
ucts. Such  a  situation  would  be  equivalent  to  continuous 
fatigue  and  would  limit  at  all  times  the  working  capacity 
of  the  muscles.  Exercise  may  be  assumed  to  bring  about 
a  more  favorable  condition  at  this  important  locality  in 
the  neuromuscular  complex. 

Still  another  result  of  training  may  be  more  extensive 
and  effective  innervation.  We  shall  make  much  of  this 
if  we  accept  the  Lucas  doctrine  of  the  fractional  response 
of  muscles.  According  to  this  view,  the  muscle  which  has 
not  been  much  used  contains  elements  which  are  not 
accessible  to  stimulation  under  any  ordinary  state  of 
affairs.  With  regular  use  the  number  of  these  idle  fibers 
may  very  likely  be  steadily  reduced  and  a  corresponding 
increase  of  force  and  endurance  realized.  The  defect 
overcome  may  be  at  the  end-plates  or  it  may  be  in  the 
central  nervous  system.  If  it  was  originally  at  the  end- 
plates,  we  may  picture  the  perikarya  which  preside  over 
the  untrained  muscle  as  being  all  active,  but  unable  to 
call  portions  of  it  into  contraction.  If  it  was  central,  we 
are  to  conceive  of  idle  perikarya  among  those  which  are 
at  work,  each  unemployed  neuron  having  a  cluster  of 
dependent  muscle-fibers  which  remain  at  rest. 

So  far  we  have  spoken  of  peripheral  improvements, 
save  that  in  the  last  instance  we  have  introduced  the  idea 
of  a  possible  central  factor.  We  have  recognized  the  ad- 
vantages accruing  (1)  from  the  actual  growth  Of  the 
muscles,  (2)  from  improved  contractile  substance,  (3) 
from  more  reliable  end-plates,  and  (4)  from  better  "team 
work"  among  the  neurons  governing  single  muscles. 
Now,  by  a  simple  extension  of  the  last-named  factor,  we 


THE    NEUROMUSCULAR    SYSTEM:    FATIGUE  113 

may  include  the  gain  through  coordination.  This  is  what 
we  mean  by  acquiring  skill.  In  all  Vjut  the  most  elemen- 
tary movements  the  best  combinations  of  contractions 
on  the  part  of  different  muscles  have  to  be  secured  by 
practice.  The  physiologic  change  which  makes  the 
gain  possible  must  consist  in  the  establishment  of  new 
ties  between  the  various  groups  of  neurons  at  all  levels 
in  the  central  nervous  system. 

Better  coordination  means  better  economy  of  force. 
When  one  is  riding  a  bicycle  in  the  early  days  of  the  ex- 
perience much  strength  is  wasted.  The  foot  which  is 
coming  up  resists  the  foot  which  is  going  down.  This  is  a 
type  of  an  interference  which  is  widespread  where  many 
muscles  are  set  to  work  in  an  unwonted  form  of  exercise. 
When  the  "knack"  is  attained,  much  less  internal  work 
is  done  for  a  given  external  result.  This  has  been  proved 
by  measurements  of  the  respiratory  exchange  in  persons 
who  were  performing  certain  tasks  (climbing  hills,  for  in- 
stance), with  and  without  adequate  training.  It  is  alto- 
gether probable  that  in  reaching  the  full  measure  of 
economy,  precision,  and  endurance  the  cooperation  of 
the  cerebellum  is  secured. 


CHAPTER   IX 

THE  AUTONOMIC   NERVOUS   SYSTEM 

The  term  which  is  used  as  the  title  of  tliis  chapter  is 
employed  to  cover  that  part  of  the  efferent  system  which 
does  not  control  the  skeletal  muscles.  The  negative  de- 
scription seems  awkward,  but  is  nevertheless  accurate  and 
final.  It  is  equivalent  to  the  statement  that  the  autonomic 
system  regulates  the  action  of  the  heart,  the  glands,  and 
all  structures  in  which  there  is  contractile  tissue  of  the 
kind  known  as  plain,  smooth,  or  visceral  muscle.  This 
variety  of  tissue  occurs  in  the  alimentary  canal,  the 
gall-bladder,  the  urinary  bladder  and  the  ureters,  in  the 
reproductive  organs,  in  the  blood-vessels  and  lymphatics, 
and  in  the  bronchial  tubes.  It  is  also  represented,  though 
sparsely,  in  the  skin.  It  forms  the  accommodation  or 
focusing  muscle  of  the  eye  and  its  presence  in  the  iris  makes 
possible  the  familiar  changes  in  the  size  of  the  pupil. 

The  term  "autonomic"  is  akin  to  the  political  word 
"autonomy,"  and  imphes  "self-regulating."  A  contrast 
between  this  di\'ision  of  the  nervous  system  and  that 
which  governs  the  skeletal  muscles  is  suggested.  It  is  a 
common  practice  to  call  the  skeletal  muscles  "voluntary," 
and  to  regard  the  heart  and  all  the  organs  equipped  with 
plain  muscle  as  "involuntary."  The  distinction  is  as  apt 
to  mislead  as  to  be  helpful  and  it  will  not  be  insisted  upon 
here.  Of  course,  it  is  true  that  we  often  have  a  fore- 
knowledge of  the  movements  of  our  skeletal  muscles  which 
we  do  not  have  in  any  such  degree  with  respect  to  the  other 
motor  elements  in  the  body  nor  as  regards  the  behavior  of 
the  glands.  But  we  must  note  that  much  of  the  activity 
of  the  so-called  voluntary  muscles  proceeds  with  little 
conscious  attention  on  our  part   (breathing,  balancing), 

114 


THE    AUTONOMIC    NERVOUS    SYSTEM 


115 


while  we  shall  find  that  there  are  many  correspondences 
between  the  states  of  consciousness  and  the  reactions 
brought  about  through  the  autonomic  system. 

It  will  not  be  profitable  to  say  much  about  the  anatomy 
of  this  division  of  the  nervous  system.  The  details  are 
exceptionally  difficult.  One  point,  however,  must  not  be 
omitted:  so  far  as  we  know,  each  path  from  the  cord 
or  the  brain  to  any  outlying  locality  reached  by  autonomic 
influences  is  a  tandem  arrangement  of  two  orders  of 
neurons  (see  page  33).     The  neurons  of  the  first  order — 


Fig.  21. — To  contrast  the  path  to  the  skeletal  muscles,  already 
familiar,  in  which  one  neuron  extends  from  the  central  nervous 
system  to  the  contractile  structures  with  the  autonomic  path  in 
which  two  orders  of  neurons  are  employed  to  span  the  same  interval. 
Cells  of  visceral  muscle  are  represented  at  the  end  of  the  post- 
ganglionic fiber.  In  the  interest  of  simplicity  the  preganglionic  neu- 
ron is  made  to  influence  only  one  of  the  lower  order.  It  would  really 
affect  several. 


preganglionic,  as  they  are  called — have  their  perikarya 
within  the  brain  or  the  cord  and  extend  outside  to  a 
greater  or  less  distance.  They  end  by  forming  synaptic 
connections  with  neurons  of  the  second  order — post- 
ganglionic— and  these  complete  the  transmission  to  the 
secreting  or  contractile  tissues  to  be  affected.  The  syn- 
apses between  neurons  of  the  first  and  those  of  the  second 
order  are  usually  to  be  found  in  ganglia,  detached  collec- 
tions of  gray  matter  variously  situated.  Two  chains 
of  these  ganglia  are  seen  in  the  back  of  the  body  cavity, 
one  on  either  side  of  the  spinal  column.     Preganglionic 


IIG      THE    NERVOUS   SYSTEM    AND    ITS    CONSKKVATION 

fibers  reach  thcnii  from  the  neighboring  spinal  nerves,  and 
their  postganghonio  fil)ers  either  rejoin  the  spinal  nerves 
to  be  distributed  with  their  peripheral  branches  or  pass 
directly  to  endings  in  the  viscera.  These  two  chains 
with  their  connections  are  known  under  the  curious  old 
name  of  the  "sj'mpathetic  system."  The  word  used 
never  had  its  psychologic  meaning. 

"Autonomic"  is  a  more  inclusive  term  than  "sympa- 
thetic." The  sympathetic  system  is  that  part  of  the 
autonomic  receiving  preganglionic  fibers  from  the  thoracic 
and  lumbar  portions  of  the  spinal  cord.  There  are  auto- 
nomic pathwaj^s  beginning  in  the  brain  which  are  not 
reckoned  in  the  sympathetic  system,  and  there  are  others 
at  the  lower  end  of  the  spinal  axis  which  He  outside  its 
anatomic  limits.  We  shall  not  often  have  occasion  to 
refer  to  the  sympathetic  system  apart  from  the  larger 
complex  of  which  it  is  a  fraction.  Ganglia  belonging  to  the 
autonomic  system,  but  lying  outside  the  two  sympathetic 
chains,  are  found  in  very  many  localities;  for  example, 
behind  the  eye,  in  the  walls  of  the  heart,  and  clustered 
about  the  arteries  which  supply  the  digestive  organs. 
They  are  not  to  be  confused  with  the  ganglia  connected 
with  afferent  paths,  which  are  found,  for  the  most  part, 
close  to  the  point  of  entrance  of  such  paths  into  the  central 
nervous  system. 

We  may  now  pass  to  a  condensed  statement  of  the 
operations  of  the  autonomic  system  upon  various  depart- 
ments of  the  physiologic  mechanism.  We  may  well  speak 
first  of  its  control  of  the  circulation.  This  is  exercised 
partly  through  the  cardiac  and  partly  through  the  vaso- 
motor nerves.  The  heart  is  a  muscular  pump,  and  on  the 
force  and  frequency  of  its  beat  depends  the  volume  of 
blood  sent  through  the  arteries  to  all  regions  of  the  body. 
Its  beating  is  fundamentall}^  automatic,  but  subject  to 
extensive  regulation  through  the  nerve-centers.  Auto- 
nomic paths  to  the  heart-muscle  can  be  traced  from  two 
sources.  Of  these,  the  most  conspicuous  and  the  earliest 
to  be  studied  is  represented  by  certain  fibers  in  the  large 


THE    AUTONOMIC    NERVOUS    SYSTEM  117 

nerve  known  as  the  vagus,  the  tenth  in  the  cranial  series 
(see  page  73). 

When  the  vagus  nerves  of  a  dog  are  both  cut,  it  is  com- 
monly observed  that  the  rate  of  the  heart  is  considerably 
increased.  This  is  taken  to  mean  that  a  restraining  or 
inhibitory  influence  was  previously  exerted  through  these 
nerves  upon  the  heart's  activity.  This  impression  is  con- 
firmed when  the  peripheral  end  of  one  of  the  cut  vagi  is 
subjected  to  electric  stimulation.  The  heart  may  be  made 
to  stand  still  for  some  seconds  and  the  circulation  is 
stopped.  This  would  kill  the  dog  in  a  short  time  if  it 
could  be  continued,  but  it  cannot;  the  heart  is  said  to 
"escape,"  that  is,  to  resume  its  beating  in  spite  of  con- 
tinued stimulation  of  the  vagus.  Still,  the  rate  and  force 
of  the  beat  can  be  kept  below  the  original  standard  for  an 
indefinite  time.  The  natural  conclusion  with  reference 
to  the  share  borne  by  the  vagi  in  the  government  of  the 
heart  is  that  they  contain  fibers  through  which  its  activity 
is  generally  held  in  check  and  a  reserve  for  emergencies 
guaranteed.  The  organ  may  be  assumed  to  expend  its 
power  unprofitably  when  these  fibers  have  been  cut. 

The  heart  receives  some  nerve-fibers  in  addition  to  those 
which  reach  it  by  way  of  the  vagi.  These  others  come 
from  the  sympathetic  ganglia  near  its  own  level  in  the 
thorax.  They  are  not  easily  picked  up  for  stimulation 
in  the  living  animal,  but  when  the  experiment  is  success- 
ful they  are  found  to  have  an  effect  just  opposite  to  that 
which  has  been  described.  They  furnish  paths  through 
which  impulses  can  be  sent  to  quicken  and  make  more 
forcible  the  beating  of  the  heart.  The  branches  coming 
to  the  heart  from  the  sympathetic  ganglia  are  called  the 
cardiac  accelerators.  Simultaneous  stimulation  of  the 
vagus  and  an  accelerator  path  brings  out  the  fact  that  the 
two  sets  of  fibers  are  true  antagonists;  the  influence  of 
the  one  can  be  neutralized  through  the  other. 

This  is  a  type  of  nervous  organization  which  we  find 
again  and  again  in  the  body.  Antagonistic  nerves  are 
almost  as  obvious  as  antagonistic  muscles.     Being  pro- 


118     THE    NERVOUS   SYSTEM   AND   ITS   CONSERVATION 

vided  with  such  a  double  supply,  the  heart  may  be  made 
to  beat  faster  through  the  spurring  which  it  receives  from 
its  accelerators,  or  a  similar  ciuickening  of  its  rate  may 
represent  merely  a  lessening  of  the  habitual  vagus  inhibi- 
tion. A  slowing  heart  may  be  exhibiting  the  results  of 
cessation  of  the  accelerator  prodding,  or  the  case  may  be 
one  of  intensified  inhibition.  On  the  whole,  it  is  held 
that  the  vagus  mechanism  is  the  more  important  of  the 
two. 

Vasomotor  Control. — A  prominent  department  of  the 
autonomic  system  is  that  devoted  to  the  regulation  of 
local  blood-flow  by  bringing  about  changes  in  the  diameter 
of  the  small  arteries  and  veins.  The  blood-vessels  of  micro- 
scopic size  are  relatively  rich  in  muscular  elements.  The 
majority  of  these  contractile  cells  are  placed  with  their 
long  axes  at  right  angles  to  the  course  of  the  blood,  and 
the  natural  result  of  their  contraction  is  to  diminish  the 
bore  of  the  vessels  and  to  reduce  the  flow  through  them. 
As  the  situation  is  now  pictured,  it  is  supposed  that  the 
larger  arteries  and  veins  shrink  and  swell  as  the  pressure 
of  the  blood  within  falls  or  rises,  but  that  the  very  slender 
vessels  of  both  classes  contract  and  relax  by  virtue  of 
the  living  tissue  contained  in  their  walls  and  in  response 
to  impulses  sent  from  the  central  nervous  system.  Nerve- 
fibers  conveying  impulses  to  the  muscular  coats  of  the 
small  blood-vessels  are  called  vasomotor  fibers.  Like 
those  which  end  in  the  heart,  they  are  of  two  classes. 

The  first  kind  of  vasomotor  fibers  to  be  observed  at 
work  were  those  which  we  now  call  the  vasoconstrictors. 
By  this  term  we  designate  fibers  by  means  of  which  a  nar- 
rowing of  the  vessels  can  be  secured.  They  have  con- 
nections such  that  when  they  are  stimulated  the  contrac- 
tile elements  in  the  walls  of  the  arteries  or  veins  to  which 
they  extend  are  shortened.  The  "tone"  of  the  vessels 
in  question  is  said  to  be  increased.  A  diminished  blood- 
flow  through  the  parts  reached  by  the  arteries  or  drained 
by  the  veins  is  to  be  expected.  Vasoconstriction  is  the 
usual  effect  when  the  peripheral  portion  of  a  nerve  chosen 


THE  AUTONOMIC  NERVOUS  SYSTEM       119 

at  random  is  subjected  to  stimulation.  When  such  a  nerve 
is  cut  the  vessels  in  the  field  of  its  distribution  are  gener- 
ally found  to  dilate;  this  is  taken  to  show  that  a  tonic 
influence  was  being  exerted  through  the  vasoconstrictor 
fibers  and  that  this  has  ceased  with  the  interruption  of  their 
continuity. 

We  speak  of  a  vasoconstrictor  center  in  the  medulla. 
There  is  evidence  that  impulses  are  normally  flowing  at 
all  times  from  a  certain  region  within  this  section  of  the 
brain  to  hold  the  small  blood-vessels  in  most  parts  of  the 
body  in  a  state  of  contraction  beyond  that  which  is  natural 
to  them.  Three  orders  of  neurons  must  be  required  to 
accomphsh  the  purpose:  first,  those  which  descend  from 
the  medulla  to  end  by  synapses  against  preganglionic 
neurons  in  the  cord;  second,  these  same  preganglionic 
neurons,  whose  axons  run  to  detached  gangha  in  the  sym- 
pathetic chains  or  elsewhere;  and  third,  postganghonic 
fibers  extending  from  the  ganglia  to  the  blood-vessels. 
Destruction  of  the  well-defined  vasoconstrictor  center  in 
the  medulla  results  in  a  universal  slackening  of  the  essen- 
tial vascular  tone  in  the  entire  body. 

The  second  variety  of  vasomotor  fibers  is  not  so  often 
seen  'in  action.  They  are  the  vasodilators,  fibers  which, 
when  stimulated,  cause  the  enlargement  of  the  vessels  and 
so  of  the  blood-stream  in  the  parts  to  which  they  lead. 
This  action  is  an  inhibition.  It  was  first  demonstrated 
in  the  case  of  a  sinall  nerve  known  as  the  chorda  tympani, 
which  makes  a  connection  with  one  of  the  salivary  glands. 
Cutting  the  chorda  tympani  has  little  effect  on  the  circu- 
lation in  the  gland,  but  when  the  nerve  is  stimulated  the 
gland  becomes  flushed  and  swollen.  At  the  same  time  the 
outflow  through  the  veins  is  obviously  increased;  it  is  said 
that  the  blood  coming  away  no  longer  shows  the  darkened 
color  usual  to  venous  blood,  but  is  as  bright  as  the  arterial. 
The  experiment  has  shown  that  in  this  nerve  at  least  there 
are  fibers  through  which  an  increase  of  the  volume  of  the 
local  circulation  can  be  brought  about. 

There  are  other,  though  not  many,  examples  ofvaso- 


120      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

dilator  action  on  the  part  of  particular  nerves.  There 
is  sufficient  rcnison  for  the  belief  that  in  many  mixed  nerves 
vasodilator  fillers  really  accompany  the  vasoconstrictors, 
but  that  the  working  of  the  first  class  is  masked  in  our 
ordinary  laboratory  trials  by  the  greater  effect  of  their 
antagonists.  When  we  stimulate  a  nerve  we  are  obliged 
to  impress  the  stimuli  upon  all  the  fibers  in  it;  in  the  Uving 
body  there  is  no  such  necessity.  Under  conditions  spe- 
cially devised  it  is  possible  to  obtain  results  which  lead 
to  the  view  that  vasodilators  are  widely  distributed  and 
bear  a  considerable  part  in  the  regulation  of  the  circulation. 
Their  existence  in  connection  with  skeletal  muscles,  glands, 
the  skin  of  the  face,  and  the  tissues  of  the  genitals  is  well 
recognized. 

We  are,  therefore,  to  think  of  the  nervous  sj^stem  as 
having  two  routes  by  which  it  can  influence  the  beat  of  the 
heart  and  two  by  which  it  can  modify  the  degree  of  con- 
traction of  the  blood-vessels.  There  is  the  possibility  of 
inhibition  of  the  heart  through  the  vagi  and  the  possibil- 
ity of  inhi])iting  the  tone  of  blood-vessels  through  the 
dilators.  The  heart  can  be  driven  to  greater  contractile 
activity  by  means  of  its  accelerators  and  the  blood-vessels 
can  be  contracted  in  a  greater  degree  by  the  vasocon- 
strictors. The  correspondence  is  helpful,  even  though  we 
have  to  do  in  the  one  case  with  rhythmic,  and  in  the  other 
with  sustained,  action.  But  it  is  only  fair  to  add  that  in 
the  case  of  the  heart  the  inhibitory  mechanism  appears 
to  be  more  important  than  its  antagonist,  while  the  vaso- 
constrictors seem  to  have  a  more  conspicuous  influence 
than  do  the  vasodilators  in  securing  the  proper  distribu- 
tion of  the  blood.  In  short,  the  heart  is  most  of  the  time 
inhibited  to  some  extent,  while  the  blood-vessels  are  most 
of  the  time  definitely  contracted.  Their  condition  is  such 
that  they  may  be  contracted  more,  or  more  relaxed,  as  a 
result  of  variations  in  the  activity  of  the  vasoconstrictor 
center. 

The  chief  value  of  the  nervous  equipment  of  the  heart 
must  lie  in  making  it  possible  to  speed  up  the  circulation 


THE    AUTONOMIC    NERVOUS   SYSTEM  121 

when  there  is  a  call  for  more  oxygen  and  for  the  rapid 
removal  of  wastes  from  the  tissues.  Muscular  activity 
is  the  occasion  when  this  need  is  most  urgent  and  when 
the  response  of  the  heart  is  most  striking.  In  a  more 
moderate  degree  the  heart  is  required  to  maintain  a  more 
active  circulation  after  the  taking  of  a  full  meal.  The 
combined  effect  of  vigorous  exercise  and  a  recent  dinner 
probably  constitutes  a  maximal  demand  upon  the  reserve 
power  of  the  heart. 

Vasomotor  adaptations  serve  to  satisfy  local,  as  con- 
trasted with  general,  needs.  Activity  in  any  limited 
portion  of  tissue,  as  in  a  gland  or  in  a  small  group  of 
muscles,  can  be  supported  without  making  an  appeal  to 
the  heart.  It  is  only  necessary  that  the  blood-vessels 
leading  to  the  active  region  shall  be  dilated  so  as  to  con- 
duct thither  a  somewhat  larger  share  than  usual  of  the 
total  stream.  This  circumscribed  increase  in  blood- 
supply  will  mean  a  certain  subtraction  from  the  flow  in 
other  directions,  but  if  a  single  small  gland  is  to  be  com- 
pared with  all  the  rest  of  the  body  we  must  admit  that 
the  loss  shared  by  so  many  organs  may  easily  be  imper- 
ceptible in  any  one  of  them.  When  a  relatively  large 
mass  of  tissue  has  its  vessels  dilated,  there  is  often  a  com- 
pensatory construction  somewhere  else.  The  foremost 
illustration  of  this  principle  is  found  in  the  reciprocal 
relation  between  the  surface  of  the  body  and  the  deeper 
parts.  We  observe  that  heat  applied  to  the  skin  increases 
the  flow  of  blood  through  the  heated  area;  reason  and 
experience  both  show  that  when  such  an  increase  occurs 
the  internal  vessels  must  be  less  dilated  than  they  were 
before. 

Some  space  may  well  be  devoted  to  a  discussion  of  the 
effects  of  external  temperature  on  the  distribution  of  the 
blood.  When  we  have  evidence  of  increased  blood-content 
in  any  part  we  say  that  a  congestion  exists.  When  the 
skin  is  flushed  as  a  result  of  being  warmed,  it  may  be  said 
to  be  congested,  though  the  word  is  so  often  used  of  ab- 
normal conditions  that  we  may  prefer  the  milder  term 


122      THE    NERVOUS    SYSTEM   AND    ITS    CONSERVATION 

"hyperemic."  Congestions  arc  of  two  types,  active  and 
passive.  In  both  there  is  a  local  excess  of  blood,  but  in  the 
active  form  it  is  blood  swiftl}'  flowing  through  widely 
opened  vessels,  while  in  the  passive  sort  it  is  blood  arrested 
or  dammed  up,  a  state  which  naturally  suggests  a  venous 
obstruction. 

The  congestion  produced  in  the  skin  by  heat  is  active 
in  character.  A  glance  at  the  swollen  veins  convinces 
one  that  they  are  carrying  a  great  volume  of  blood  out  of 
the  flushed  region.  The  reaction  is  a  serviceable  one;  it 
tends  to  rid  the  body  of  heat,  both  by  increasing  radiation 
and  conduction  from  the  skin  and  by  sustaining  the  activ- 
ity of  the  sweat-glands,  which  at  such  a  time  secrete  much 
water  to  be  evaporated.  If  the  external  temperature  is  so 
high  that  the  body  is  cooler  than  its  surroundings,  the 
radiation  and  conduction  transfers  may  be  reversed,  but 
it  remains  important  to  have  an  abundant  circulation  in 
support  of  the  secretion  of  sweat.  There  is  at  present 
some  doubt  as  to  how  far  the  increase  of  blood-flow  which 
heat  produces  in  the  skin  is  a  reflex  and  how  far  a  direct 
effect  of  the  high  temperature. 

When  the  skin  is  moderately  cooled,  it  becomes  pale, 
the  obvious  sign  of  diminished  blood-flow.  This  prevents 
a  wasteful  loss  of  heat  to  the  exterior  and  so  conserves  the 
bodily  resources.  But  everyone  knows  that  more  pro- 
nounced cooling  will  shortly  induce  a  reddening.  How 
does  the  redness  produced  by  cold  differ  from  that  pro- 
duced by  heat?  Investigation  of  this  question  is  easily 
conducted.  If  one  hand  is  put  into  very  cold  water  and 
the  other  into  water  as  hot  as  can  be  borne,  both  hands 
will  be  red,  but  certain  differences  will  be  quickly  apparent. 
It  has  been  said  that  the  veins  in  the  heated  hand  are 
swollen;  in  the  chilled  hand  they  are  small  and  dark.  This 
fact,  taken  in  connection  with  the  tendency  of  the  cold 
skin  to  become  bluish,  shows  that  the  congestion  produced 
by  cold  is  of  a  passive  nature.  Much  blood  is  in  the  area, 
but  it  is  making  only  slow  progress  through  it.  The  con- 
dition is  best  accounted  for  on  the  theory  that  a  marked 


THE    AUTONOMIC    NERVOUS    SYSTEM  123 

contraction  has  occurred  in  the  microscopic  veins,  holding 
back  the  blood  in  the  capillaries,  which  accordingly  swell 
even  though  the  arteries  leading  to  them  may  be  below 
their  average  size  at  the  time.  (It  is  the  amount  of  blood 
in  the  capillaries  which  determines  the  color  of  the  surface.) 

The  capacity  of  the  vasomotor  system  to  make  appro- 
priate responses  to  changes  of  external  temperature  is  far 
from  equal  in  different  subjects.  What  we  call  "vital 
resistance" — the  power  to  withstand  exposure  without 
ill  effects — must  depend  largely  upon  the  extent  of  this 
capacity.  It  is  probable  that  the  variable  feature  is  not 
so  much  in  the  execution  of  the  primary  reaction  to  weather 
changes,  as  in  the  reliability  of  the  secondary  adjustment, 
the  promptness  and  vigor  of  the  rebound  to  normal  vaso- 
motor conditions  after  a  disturbance.  The  person  who 
quickly  develops  a  "glow"  after  a  cold  bath  is  a  Uving 
demonstration  of  such  a  vasomotor  resilience,  and  we  know 
that  such  a  person  is  not  likely  to  take  cold  or  to  be  other- 
wise upset  after  being  caught  in  a  shower  or  obliged  to  sit 
in  a  chilly  place.  Still  we  must  not  fail  to  reckon  with  other 
factors  than  the  vasomotor  when  we  compare  susceptibili- 
ties; there  are  always  chemical  as  well  as  mechanical  differ- 
ences between  two  human  bodies,  and  the  bacteriologist 
refers  to  peculiarities  of  chemical  endowment  when  he 
speaks  of  the  superior  resistance  of  this  or  that  man  to 
infecting  agents.  It  is  well  for  us  to  keep  both  considera- 
tions in  sight.  If  two  men  fall  through  the  ice  and  both 
escape  unfortunate  consequences,  it  is  entirely  con- 
ceivable that  the  immunity  in  one  case  may  be  due  to 
vasomotor  reactions  which  guard  against  the  persistence 
of  conditions  which  invite  infection,  and  in  the  other  to 
specific  properties  of  the  blood. 

Something  should  be  said  of  the  vasomotor  adjustment 
for  changes  in  position.  This  is  a  matter  often  ignored 
by  the  writers  of  physiologic  text-books,  but  it  does  not 
require  much  reflection  to.  convince  one  that  it  is  of  high 
importance.  The  inevitable  influence  of  gravity  on  the 
blood  is  to  add  to  the  pressure  in  all  vessels  below  the 


124      THE    NERVOrS    SYSTEM    AM)    ITS    COXSEHVATIUN 

heart  and  to  subtract  from  the  pressure  in  those  above  the 
level  of  that  organ.  The  actual  pressui'c  of  the  blood  in 
any  vessel  is  the  resultant  of  a  certain  quantity  referable 
to  the  energy  of  the  heart-beat  plus  or  minus  a  quantity 
due  to  the  elevation  of  the  locality  as  compared  with  that 
of  the  heart.  If  the  body  were  always  erect,  the  situation 
might  be  met,  one  may  suppose,  by  th(^  development  of 
thicker  and  less  yielding  walls  in  the  vessels  of  the  lower 
extremities,  but,  in  reality,  there  has  to  be  provision  for 
changes  from  the  horizontal  to  the  upright  position,  and 
even  for  bringing  the  head  to  occupy  the  lowest  place. 

When  a  man  rises  from  his  l^ed  he  does  not  normally 
feel  any  distinct  faintness  or  dizziness  as  he  would  if  there 
were  a  serious  impairment  of  blood-supply  to  his  brain. 
Yet  the  tendency  for  the  blood  to  forsake  the  higher  arcs 
of  the  circulation  and  to  distend  the  lower  ones  must  be  a 
very  positive  force.  It  is  manifest  when  there  is  actual 
faintness,  the  indi\ddual  being  comparatively  comfortable 
while  lying  down,  though  he  may  be  utterly  unable  to  sit 
up.  We  have  to  conclude  that  in  health  the  shifting  of 
the  ■  blood  is  prevented  with  singular  efficiency  by  the 
establishment  of  a  higher  vasomotor  tone  in  the  vessels  on 
which  the  added  pressure  falls.  This  is  one  of  the  first 
functions  to  fail  when  disturbing  conditions  arise;  it  is 
the  lack  of  this  reaction  which  "confines  one  to  his  bed" 
when  sick.  Compensation  for  the  head-down  position 
probably  never  comes  to  be  perfect.  We  see  even  in 
acrobats  of  long  experience  the  intense  flushing  of  the 
face  when  the  head  is  hanging  down,  as  in  swinging  by 
the  feet  from  a  trapeze. 

We  have  seen  that  the  vasomotor  system  makes  im- 
portant and  widespread  changes  in  the  distribution  of  the 
blood  under  the  influence  of  changes  of  the  external  tem- 
perature, and  that  it  exercises  its  powers  to  guard  against 
injurious  modifications  in  distribution  when  the  posture  is 
shifted.  We  have  also  stated  the  general  principle  that 
this  system  dilates  (or  permits  the  relaxation  of)  vessels 
at  any  center  of  unusual  activity.     It  would  be  easy  to 


THE    AUTONOMIC    NERVOUS    SYSTEM  125 

extend  this  discussion  by  including  other  instances  of 
vasomotor  accommodation.  A  most  interesting  and  sug- 
gestive case  is  the  reaction  which  accompanies  sleep. 
This  and  the  reciprocal  case  of  the  reaction  that  comes 
with  fixation  of  attention  may  be  left  to  be  dealt  with  in 
another  chapter. 

Other  Autonomic  Functions. — Besides  regulating  the 
beat  of  the  heart  and  the  local  blood-supply,  the  autonomic 
fibers  convey  impulses  to  contractile  structures  not  related 
to  the  circulatory  system.  The  government  of  the  alimen- 
tary canal  is  carried  on  by  means  of  such  paths.  Here, 
as  with  the  heart,  there  is  a  resident  automatic  power  in 
the  walls  of  the  tube,  and  what  the  nervous  system  does 
is  to  modify  the  intrinsic  tendency  to  tonic,  rhythmic, 
and  progressive  (peristaltic)  action.  A  long  time  ago,  in 
the  present  treatment,  it  was  said  that  inhibitory  rather 
than  excitatory  influences  are  the  rule  in  this  department 
of  nervous  control.  It  will  be  convenient  to  discuss  the 
extent  of  autonomic  government  of  the  digestive  tract 
when  we  come  to  the  abnormalities  observed  in  the 
neurasthenic.  Autonomic  impulses  to  the  bladder  and 
reproductive  organs  are  apt  to  be  excitatory,  though  here 
again  the  double  possibihty  of  reinforcement  and  inhibi- 
tion remains. 

A  division  of  the  autonomic  system  which  is  of  minor 
significance,  but  interesting  because  it  is  curious,  is  the 
pilomotor  part.  Under  this  head  we  include  the  fibers 
which  go  to  the  scattering  development  of  plain  muscle 
found  in  the  skin.  The  contractile  elements  so  placed  are 
attached  to  hairs  which  may  be  rudimentary  and  scarcely 
noticeable.  When  the  muscle-cells  contract  under  nervous 
influence,  either  erection  of  the  hairs  or  the  risings  of  the 
skin  known  as  "goose-flesh"  may  be  caused.  Occasions 
on  which  the  hair  "stands  on  end"  are  apparently  rare  in 
human  experience,  but  they  are  common  enough  in  the 
life  of  the  cat.  This  animal  has  an  excellent  pilomotor 
system. 

Of  more  importance  is  glandular  control.     The  auto- 


120      THE    NERVOUS   SYSTEM   AND    ITS    CONSERVATION 

nomic  system  includes  nerve-paths  of  the  standard  type 
(prcsanjiUonic  and  postgangUonic  fibers)  to  many  organs 
of  secretion.  This  is  conspicuously  the  case  with  the 
sweat-glands.  It  is  true,  too,  of  the  tear-glands,  the  sali- 
vary glands,  and  those  in  the  lining  of  the  stomach.  It  is 
certainly  true  of  the  adrenal  bodies  and  probably  of  the 
pancreas.  There  is  less  certainty  regarding  a  direct 
nervous  control  of  the  intestinal  glands,  the  liver,  and  the 
kidney's.  When  glands  are  active  it  is  to  be  expected  that 
vasomotor  support  will  be  given  to  them  through  the  wide 
dilation  of  their  blood-vessels.  But  the  kind  of  nervous 
control  of  which  we  are  now  speaking  is  believed  to  be 
exerted  upon  the  epitheUal  cells  forming  and  cUscharging 
the  product.  Typic  secretory  activity  may  be  promoted 
in  two  waj^s  by  the  autonomic  system:  by  this  direct 
stimulation  of  the  working  cells  of  the  gland  and,  indi- 
rectly, by  the  enlisting  of  the  vasomotors  to  secure  a  freer 
circulation.  In  some  glands — for  example,  the  kidney — 
it  is  the  volume  of  the  blood-fiow  on  which  the  performance 
of  the  gland  chiefly  depends.  When  this  is  the  case  it  be- 
comes difficult  to  decide  whether  government  of  the  other 
order,  that  is,  by  true  secretory  fibers,  surely  exists. 


CHAPTER  X 
THE   CEREBRUM 

A  STUDY  of  comparative  anatomy  shows  that,  on  the 
whole,  there  is  a  gradation  in  the  development  of  the 
cerebrum  which  corresponds  fairly  well  with  the  degree  of 
intelligence  and  the  variety  of  reaction  which  different 
animals  exhibit.  In  the  brain  of  man  this  division  reaches 
its  most  conspicuous  rank.  For  at  least  a  hundred  years 
the  correlation  of  intelligence  with  the  cerebral  evolution 
and  especially  with  the  extent  of  the  cortex  has  been 
universally  accepted.  It  is  said  that  only  two  animals 
have  cerebral  hemispheres  more  massive  than  those  of 
man.  These  are  the  elephant  and  the  whale;  in  both, 
the  great  size  of  the  body  removes  the  brain  from  any 
comparison  with  that  of  man.  In  fact,  the  brain  of  the 
whale  is  relatively  small. 

Starling  says  that  in  proportion  as  the  cerebrum  be- 
comes prominent,  the  possibility  of  predicting  what  re- 
sponse will  follow  the  giving  of  a  certain  stimulus  dimin- 
ishes. The  animal  is  less  and  less  machine-like.  This  is 
closely  connected  with  the  fact  that  two  animals  of  the 
same  species  can  show  individual  traits  to  an  extent  which 
is  determined  by  the  importance  assumed  by  the  cerebrum 
in  the  reactions  of  that  species.  One  rabbit  does  not  differ 
in  very  many  respects  from  another;  two  cats  are  quite 
unlike  and  may  be  said  to  have  character  or  personality. 
In  Chapter  III  the  point  was  made  that  the  higher  type 
of  nervous  system  is  that  in  which  individual  as  well  as 
racial  acquisitions  are  stored.  We  may  now  add  that 
such  storage  is  the  particular — though  perhaps  not  the 
exclusive — work  of  the  cerebrum. 

If  two  persons  could  exchange  their  spinal  cords, 
both  being  in  good  health,  it  does  not  appear  that  the 

X27 


r_*8    Till-:  .NKRvurs  system  axd  its  coxservatiox 

exchange  would  be  attended  by  any  remarkable  gain  or 
loss  to  cither.  The  slight  and  liniit(>d  spinal  reflexes  would 
not  be  likely  to  be  at  all  strange  or  unfamiliar  to  the  new 
possessors  of  the  transferred  equipnuMit.  If  each  could 
now  take  for  his  own  the  medulla  of  his  fellow,  he  might 
notice  a  certain  strangeness  in  his  reactions.  Vasomotor 
idiosyncrasies  might  be  realized.  The  heart  might  alter 
its  average  rate.  Experience  might  reveal  changes  in  the 
capacity  of  the  digestive  system  under  new  central 
government.  Now,  if  the  cerebellum  were  also  to  be 
carried  over  from  A  to  B  and  the  corresponding  part 
removed  from  B  and  given  to  A,  the  results  would  prob- 
ably be  much  more  positive.  Peculiarities  of  gait,  accom- 
plishments or  shortcomings  in  the  line  of  equilibration, 
skill  in  dancing  or  swimming — any  of  these  might  go  with 
one  cerebellum  to  the  new  owner. 

The  paragraph  above  suggests  what  is  undoubtedly 
true  of  man,  that  some  acquisitions  are  registered  in  the 
cerebellum  if  not  lower  down  in  the  nervous  system.  But 
when  all  allowance  has  been  made  for  this  we  feel  sure 
that  the  man  who  had  surrendered  his  spinal  cord,  his 
medulla,  and  his  cerebellum  to  another,  receiving  alien 
structures  in  their  stead,  would  still  be  essentially  him- 
self. One  almost  shrinks  from  contemplating  the  imagin- 
ary exchange  of  one  cerebrum  for  another.  To  do  this 
must  be  in  a  most  literal  sense  to  "give  one's  self  away." 
So  far  as  we  can  see,  the  stock  of  memories  and  associa- 
tions which  A  regarded  as  exclusively  his  would  begin  to 
determine  the  behavior  of  the  organism  still  wearing  the 
outward  appearance  of  B. 

This  fabulous  presentation  merely  enforces  the  conten- 
tion of  Loeb  that  the  cerebrum  is  the  chief  organ  of  asso- 
ciative memory.^  Animals  in  which  it  is  not  much  de- 
veloped have  little  capacity  to  learn  anything  by  expe- 
rience. In  proportion  as  it  becomes  dominant  in  the 
nervous   system,   memory   becomes   the   basis   of  action 

*  "Comparative  Physiology  of  the  Brain"  (in  Science  Series), 
New  York,  1900. 


THE    CEREBRUM  129 

and  individuality  becomes  inevitable.  Memory  is  used 
in  two  senses.  Speaking  subjectively,  we  use  it  to  mean 
conscious  recollection.  We  can  use  it  in  a  purely  objec- 
tive way  to  mean  no  more  than  the  modification  of 
reactions  resulting  from  individual  contacts  with  the 
environment.  When  we  say  that  "the  burnt  child  dreads 
the  fire"  we  usually  mean  that  the  child  recalls  with  dis- 
tress an  unfortunate  occurrence  in  its  past.  But  the  con- 
dition can  be  indicated  in  quite  another  way.  We  may  say 
that  the  nervous  system  of  the  child  has  been  so  altered 
by  a  past  impression  upon  it  that  it  will  cause  the  child 
to  draw  back  from  the  fire.  A  type  of  action  is  impHed 
which  is  essentially  reflex. 

The  boy,  like  the  moth,  may  be  attracted  by  the  flame 
until  the  negative  reaction  has  been  established;  the 
difference  between  the  two  nervous  systems  compared 
lies  to  a  great  extent  in  the  capacity  of  the  higher  one  to 
be  modified  by  use,  the  lower  one  persisting  in  its  heredi- 
tary response  regardless  of  consequences.  The  burnt 
moth  probably  does  not  "dread  the  fire"  in  either  the 
psychologic  or  the  physiologic  sense.  The  contrast  set 
forth  is  that  between  a  system  without  any  part  closely 
corresponding  to  a  cerebrum  and  one  in  which  this  de- 
partment is  dominant. 

The  general  conception  outlined  is  justified  by  the 
results  of  experiments  in  which  animals  of  various  kinds 
are  deprived  of  their  cerebral  hemispheres  and  kept  alive 
for  observation.  The  consequences  of  the  loss  are  grave 
just  in  proportion  to  the  part  played  by  individual  ex- 
perience in  the  government  of  the  organism.  Most  fishes 
survive  the  operation  with  no  clear  sign  of  deficiency. 
When  this  is  not  strictly  true  it  is  because  the  particular 
fish  studied  has  been  one  which  was  regulated  in  its  move- 
ments by  the  impulses  derived  from  the  organ  of  smell. 
It  must  not  be  forgotten  that  this  sense  organ  and  no 
other  is  detached  from  the  remainder  of  the  nervous 
system  when  the  cerebrum  is  destroyed.  It  is  said  that 
sharks,  which  have  been  made  "decerebrate,"  as  the  term 


130      THE    NERVOUS   SYSTEM    AND    ITS    CONSERVATION 

goes,  are  very  sluggish.  But  this  docs  not  mean  that  they 
were  greatly  dependent  upon  the  organization  of  the 
cerebrum;  they  can  be  just  as  seriousl}'-  ai'fccted  if  their 
olfactory  receptors  are  destroyed,  the  cerebrum  remain- 
ing intact. 

A  frog  is  regarded  as  a  higlier  animal  than  a  fish.  A 
decerebrate  frog,  however,  departs  so  slightly  from  a 
normal  one  as  to  force  us  to  conclude  that  here,  as  in  the 
fish,  the  cerebrum  has  no  important  influence  on  the  be- 
havior of  the  animal  under  the  ordinary  conditions  of 
life.  It  is  commonly  stated,  however,  that  there  are  real 
points  of  difference  between  normal  and  decerebrate  frogs. 
The  latter  are  entirelj^  able  to  swim  and  hop,  but  they 
will  not  save  themselves  from  death  in  a  pan  of  water 
when  it  is  slowly  warmed.^ 

The  classic  instance  of  the  profound  effects  following  the 
removal  of  the  cerebrum  from  an  animal  of  high  grade 
was  afforded  by  the  experiments  of  Flourens,  in  France, 
early  in  the  nineteenth  century.  He  subjected  pigeons 
to  the  operation,  which  is  rather  a  simple  one  to  perform 
upon  the  bird.  The  descriptions  which  he  gave  have 
been  modified  by  modern  students  to  make  allowance  for 
the  well-marked  recovery  of  pigeons  from  the  immediate 
shock  of  the  procedure.  In  this  case,  as  in  that  of  the 
cerebellum,  it  is  only  the  lasting  consequences  of  the  loss 
that  we  have  a  right  to  emphasize.  Observers  have  not 
been  wholly  agreed  concerning  the  nature  of  the  deficiency 
in  all  its  details,  but  it  seems  safe  to  say  that  a  pigeon 
without  a  cerebrum  gives  no  further  sign  of  memory  or 
feeling. 

To  see  such  a  pigeon  is  an  instructive  experience,  and 
especially  when  the  spectator  takes  account  of  his  own 
emotional  reaction.     He  is  hkely  to  anticipate  that  he 

1  Burnett  (American  Journal  of  Physiology,  1912,  xxx,  80)  has 
observed  that  decerebrate  frogs  definitely  lack  the  power  shown  by 
the  intact  animals  to  become  "used  to"  certain  pathways.  A  trace 
of  adaptation  on  the  part  of  individuals  to  their  surroundings  seems, 
therefore,  to  be  represented  in  the  cerebral  equipment  of  these 
animals. 


THE   CEREBRUM  131 

will  feel  pity  for  the  mutilated  animal.  Instead,  he  cannot 
watch  it  long  without  finding  it  amusing.  He  becomes 
convinced  that  it  is  not  a  sensitive  and  suffering  creature, 
but  an  elaborate  mechanical  toy.  It  adjusts  itself  to 
external  conditions  with  great  success  so  far  as  the  imme- 
diate exigency  is  concerned,  but  with  no  anticipation  of 
the  future  nor  reminiscence  of  the  past.  In  default  of 
stimulation  it  is  relatively  inert.  It  is  customary  to  say 
that  it  does  nothing  spontaneously.  The  word,  however, 
is  a  vague  one  and  may  well  be  avoided.  An  action  is 
called  "spontaneous"  when  we  cannot  tell  how  it  was 
caused.  Some  actions  of  the  decerebrate  bird  may  be 
placed  in  this  class. 

A  pigeon  without  a  cerebrum  can  be  kept  alive  for 
weeks,  but  only  by  constant  care.  It  will  not  find  food 
or  water  for  itself,  though  they  may  be  placed  in  its  cage. 
In  flying  and  walking  it  passes  around  obstacles,  but  all 
the  evidence  goes  to  show  that  there  is  no  appreciation 
of  the  objects  in  its  path.  Another  pigeon  exists  for  it 
simply  as  a  mass  of  matter,  with  no  more  power  to  stimu- 
late than  a  block  of  wood.  The  former  mate  or  the  young 
bird  appealing  for  food — these  are  treated  merely  as 
things  with  which  a  coUision  is  to  be  avoided.  It  is 
clear  that  the  eyes  serve  well  to  regulate  locomotion  with 
reference  to  the  surroundings,  but  they  are  deprived  of 
the  power  to  cause  any  reaction  based  upon  the  indi- 
vidual experience  of  the  bird. 

Detailed  accounts  of  the  behavior  of  the  decerebrate 
pigoen  may  be  found  in  larger  works  and  they  are  full  of 
interest.  The  main  points  to  be  insisted  on  are  (1)  that 
the  muscular  capabilities  of  the  bird  remain  little  im- 
paired in  the  absence  of  the  cerebrum,  and  (2)  that  these 
muscular  activities  no  longer  signify  that  memories 
connected  with  the  past  hfe  of  the  pigeon  are  aroused. 
It  is  probably  fair  to  claim  that  the  word  ''memory"  in 
this  statement  can  be  used  either  in  its  subjective  or  ob- 
jective sense.  Moreover,  it  is  not  only  the  previous  accu- 
mulation which  is  destroyed,  but  also  the  possibihty  of  ac- 


132      THE    NERVOUS    SYSTEM    AND    ITS    CONSIORVATION 

quiring  new  impressions  wliich  can  furnish  grounds  of 
conduct. 

The  removal  of  tiie  cerebrum  from  a  mannnal  without 
causing  the  immediate  death  of  the  animal  might  well 
seem  an  incredible  feat  of  surgery.  Nevertheless,  it  has 
succeeded  in  a  number  of  cases.  The  most  celebrated 
of  these  has  been  the  one  which  is  referred  to  as  Goltz's 
dog.  By  three  carefully  conducted  operations  the  entire 
mass  of  the  cerebral  hemispheres  and,  unintentionally, 
somewhat  more  of  the  brain  was  broken  up  and  washed 
away.  The  dog  was  kept  alive  and  narrowly  observed 
for  a  j^ear  and  a  half  after  the  final  operation.  It  was 
then  killed  and  the  autopsy  showed  the  thoroughness  of 
the  destruction.  Its  health  and  strength  had  been  de- 
clining for  some  time  before  it  was  sacrificed. 

The  decerebrate  dog  afforded  a  general  confirmation  of 
the  inferences  drawn  from  the  pigeon.  It  was  idiotic, 
but  not  crippled  in  any  department  of  its  mechanical 
activities.  A  noteworthy  fact  was  that  it  was  restless 
rather  than  sluggish.  Its  aimless  rovings  supported  the 
opinion  quite  widely  held  that  an  important  function  of 
the  cerebrum  is  to  inhibit  the  action  of  the  lower  brain 
centers.  Sometimes  the  dog  appeared  to  sleep,  but,  if 
we  are  right  in  our  interpretation,  its  waking  was  not  to 
consciousness,  but  only  to  somnambulism.  It  showed  no 
fear  or  affection.  It  would  snap  at  the  hand  of  a  tor- 
mentor, but  only  under  the  direct  stimulus  of  provocation; 
it  would  not  harbor  a  grudge  against  him. 

Concerning  the  human  being,  of  course  we  do  not  have 
evidence  from  deliberate  experiment,  but  we  have  the 
facts  in  a  vast  number  of  clinical  cases.  A  surprising  and 
instructive  one  has  been  reported  quite  recently.  Edinger 
and  Fischer^  have  described  the  condition  of  a  defective 
child  that  died  of  tuberculosis  when  nearly  four  years  old. 
It  had  made  no  appreciable  progress  in  acquiring  new 
reactions  from  the  day  of  its  birth.  It  usually  lay  in 
apparent  sleep,  seemed  to  be  blind,  and  could  not  be  said 
'  Archiv  f.  d.  ges.  Physiologie,  1913,  clii,  535. 


THE    CEREBKUM  133 

to  show  any  token  of  consciousness.  The  postmortem 
examination  showed  entire  lack  of  the  cerebral  hemi- 
spheres. 

When  we  compare  this  shocking  instance  with  the  case 
of  the  dog  or  the  pigeon,  we  are  led  to  believe  that  the 
human  cerebrum  is  of  such  overwhelming  dominance  that 
many  functions  which  in  the  lower  animals  can  be  sub- 
served by  other  parts  of  the  brain  have  been  largely  trans- 
ferred to  it.  In  man  it  is  probable  that  the  subordinate 
centers  for  the  eyes  are  incapable  of  any  extensive  or 
useful  reaction  when  their  cerebral  connections  are  severed. 
It  is  not  likely  that  the  power  to  balance  and  to  walk 
could  be  preserved  in  man  as  in  the  dog  through  the 
agency  of  the  midbrain,  cerebellum,  and  medulla  without 
the  cerebrum.  To  be  sure,  the  decerebrate  child  had 
never  learned  to  walk,  and  it  might  be  urged  that  the 
cerebrum  might  be  essential  for  the  attentive  act  of  learn- 
ing and  not  for  exercising  the  power  when  acquired.  But 
we  have  many  other  cases  in  which  the  ability  to  walk 
was  lost  when  only  a  limited  part  of  the  cerebrum  had 
suffered  injury. 

In  apes,  which  approach  the  human  type  of  organization, 
the  loss  of  a  restricted  region  from  the  cerebrum  is  said  to 
lead  to  absolute  blindness  so  far  as  can  be  determined. 
The  power  to  avoid  obstacles,  so  striking  in  the  dog  and 
the  pigeon,  entirely  disappears.  In  all  probabihty,  a 
decerebrate  human  being  would  be  deaf,  despite  the  fact 
that  the  auditory  nerve  would  retain  its  connection  with 
the  medulla  and  so  with  the  remainder  of  the  nervous 
system.  Pigeons  without  the  cerebrum  respond  to  cer- 
tain sounds  by  sluggish  movements. 

Granting,  as  we  must,  that  the  cerebrum  is  essential  to 
intelligence  and  to  all  action  based  upon  individual  ex- 
perience, we  are  at  once  led  to  inquire  wiiether  it  is  all 
alike  or  whether  particular  parts  have  particular  func- 
tions. In  other  words,  is  there  cerebral  localization  of  a 
definite  character?  This  question  was  asked  by  Flourens 
long  ago,  and  he  attempted  to  answer  it  on  the  basis  of 


134      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

further  experiments  on  pigeons.  He  came  to  believe  that 
one  part  is  like  anothcM-  and  that  the  result  of  an  injury 
is  detorniined  by  its  extent  and  not  by  its  position.  Speak- 
ing somewhat  crudely,  it  may  be  said  that  this  view  made 
the  working  of  the  brain  comparable  with  that  of  the 
Uver:  all  its  parts  were  supposed  to  be  working  in  the 
same  way  and  all  its  functions  would  suffer — quanti- 
tatively rather  than  qualitatively — from  a  circumscribed 
injury. 

From  the  time  of  Flourens  to  the  present  scientific 
opinion  has  shifted  back  and  forth  in  a  curious  manner. 
In  his  own  career  he  found  himself  called  upon  to  defend 
his  claims  against  a  school  of  ingenious  persons  who 
upheld  the  doctrine  of  a  very  precise  locaUzation  of 
cerebral  properties.  This  teaching  was  presentl}^  known  as 
phrenology^  and  attracted  much  notice.  In  the  beginning 
the  phrenologists  were  sincere  in  purpose  and  more  or 
less  scientific  in  method.  Their  successors  departed 
widely  from  the  early  traditions  of  the  school,  and  are  now 
found  in  the  purlieus  of  our  cities  along  with  palmists  and 
clairvoyants.  The  general  conception  was  beginning  to 
be  discredited  when  Holmes^  wrote  of  it  so  incisively. 
Regarding  the  claim  that  it  is  possible  to  tell  what  is 
within  the  skull  by  measuring  its  slight  convexities  and 
depressions,  he  well  said  that  this  was  like  laying  one's 
finger  on  the  iron  wall  of  a  safe  and  saying:  "Under  this 
spot  lies  a  ten-dollar  bill." 

Francis  Joseph  Gall,  the  Austrian  founder  of  phrenology, 
seems  to  have  had  little  interest  in  the  l^rain  as  related  to 
the  body,  but  much  in  its  assumed  correlation  with  men- 
tal endowments  and  defects.  He  and  his  disciple's  made 
careful  measurements  of  the  contours  of  the  head  in  all 
types  of  men,  from  the  most  gifted  to  the  most  defective 
and  depraved.     A  prominence  upon  the  surface  of  the 

'  The  article  "Phrenology"  in  the  Encj'clopedia  Britannica  can  be 
recommendod. 

2  "The  Professor  at  the  Breakfast  Table,"  Riverside  Edition, 
19O-200. 


THE    CEREBRUM  135 

skull  was  supposed  to  indicate  an  extra  cerebral  develop- 
ment beneath,  and  if  a  special  merit  or  failing  coexisted 
in  the  individual  the  notable  feature  of  the  brain  was  held 
to  be  responsible  for  it.  This  summary  statement  is 
scarcely  just  to  the  pioneers  in  phrenology,  for  they  did 
not  commit  themselves  until  they  had  a  great  mass  of 
data.  They  pubhshed  large  books,  conducted  periodicals, 
and  even  had  museums  in  which  the  comparative  study  of 
human  skulls  was  carried  on. 

A  cursory  glance  at  their  later  writings  shows  how  dis- 
ingenuous they  became.  They  showed  an  unrivaled  skill 
in  getting  around  difficulties.  A  certain  protuberance 
was  held  to  indicate  a  certain  propensity,  but  its  occa- 
sional absence  from  a  subject  in  whom  that  propensity 
was  well  marked  did  not  cause  them  any  trouble.  In 
such  a  case  they  said  that  the  subdivision  of  the  brain 
under  discussion  had  been  worn  down  by  excessive 
activity.  This  would  seem  to  require  a  plasticity  of  the 
cranial  bones  beyond  that  commonly  observed.  When 
external  measurements  were  made  upon  the  forehead  it 
was  somewhat  hard  to  allow  for  the  variable  extent  of 
the  frontal  sinuses,  cavities  which  occur  in  that  bone, 
but  they  did  not  fret  themselves  about  that. 

Phrenology  lost  the  respect  of  conscientious  men  of 
science  before  the  middle  of  the  century.  The  prevalent 
feeling  was  one  of  skepticism  regarding  all  claims  for 
localization  of  function  in  the  cerebrum.  When,  after  an 
interval,  new  ideas  concerning  the  connection  of  particular 
properties  with  particular  regions  began  to  be  advanced, 
it  was  in  a  totally  different  spirit  from  that  of  the  old 
teachings.  The  new  localization  was  of  the  control  of 
bodily  functions  and  only  guardedly  extended  to  the 
problems  of  the  mental  hfe.  The  return  to  the  behef 
that  the  cerebrum  is  not  all  ahke  may  be  said  to  date 
from  1870.  It  made  headway  rapidly  for  about  twenty- 
five  years  and  has  been  followed  by  another  reaction,  so 
that  present-day  writing  on  the  subject  is  cautious  and 
conservative. 


130      THK    XKliVorS    SYSTEM    AND    ITS    COXSKRVATION 

The  perforinances  of  the  cerebral  cortex  luive  been 
likened  to  those  of  an  orclu^stra.  The  comparison  would 
have  been  acceptable  either  to  an  old-fashioned  phrenol- 
ogist or  to  a  believer  in  the  diffuse  distribution  of  brain 
activity.  A  series  of  solos  by  different  instruments 
would  symbolize  the  phrenologic  conception;  a  harmoni- 
ous production  of  music  by  many  or  all  the  players  would 
represent  the  other  interpretation.  Local  injury,  accord- 
ing to  the  first  view,  would  be  the  silencing  of  a  solo 
instrument  and  would  cause  intervals  of  stillness  in  the 
symphony.  If  the  second  view  were  found  to  ])e  correct, 
the  local  damage  would  not  result  in  absolute  interruption 
of  the  music,  but  only  in  lessening  its  volume  and  rich- 
ness. 

It  is  difficult  to  say  exactly  what  is  meant  by  "cerebral 
localization."  In  all  probability,  the  term  does  not  mean 
the  same  to  different  people  who  use  it.  It  would  seem 
that  to  some  it  has  meant  that  definite  regions  of  the 
cortex  are  in  receipt  of  certain  impressions,  and  can,  at  a 
later  time,  give  rise  to  impulses  determined  by  these 
stored  impressions.  Descartes  must  have  had  some  such 
an  idea  as  this  when  he  likened  the  retention  of  memories 
to  the  imprint  of  a  seal  upon  wax.  Quite  another  view 
is  possible,  and,  indeed,  it  is  the  preferred  one  at  the 
present  time.  This  is  the  conception  that  a  given  func- 
tion appears  to  be  connected  with  a  given  area  simply 
because  so  many  of  the  paths  necessary  to  that  function 
he  -within  the  patch  of  cortex  in  question. 

To  appreciate  the  modern  interpretation  of  the  working 
of  the  cerebrum  it  is  necessary  to  keep  always  before  one 
the  reflex  principle.  We  readily  apply  this  principle  to 
the  spinal  cord.  Impulses  flow  in  and,  in  consequence, 
others  are  sent  out.  It  is  not  difficult  to  extend  this  to 
the  medulla,  the  midbrain,  and  the  cerebellum;  the  chief 
difference  between  the  responses  from  these  parts  and 
from  the  cord  Hes  in  the  greater  length  of  the  pathways 
pursued  by  the  impulses,  the  greater  numl)er  of  synapses 
crossed,  and  the  increased  capacity  for  variation.    When 


THE    CEREBRUM  137 

we  consider  the  cerebrum  we  are  too  apt  to  assume  that 
conditions  there  differ  radically  from  those  at  lower 
stations.  We  cannot  ignore  the  relation  of  the  cerebral 
structures  to  our  consciousness,  but  we  shall  escape  much 
confusion  if  we  hold  fast  so  far  as  we  may  to  the  reflex 
arc  as  the  fundamental  fact  in  the  organization. 

Impulses  enter  the  cerebral  cortex  from  the  afferent 
division  of  the  nervous  system  as  they  enter  other  parts 
of  the  gray  matter.  Only  here  the  direction  which  may 
be  given  to  these  impulses  is  far  less  certain  than  in  the 
lower  central  complexes.  The  net  of  pathways  has  that 
individual  character  which  has  been  emphasized,  and  be- 
cause of  this  no  two  cerebral  cortices  can  react  in  just  the 
same  manner.  The  great  number  of  simultaneous  proc- 
esses going  on  in  the  cerebrum  results  in  apparent  col- 
lisions and  interferences  which  make  it  still  harder  to 
predict  the  effect  produced  by  a  stimulus — be  it  sight, 
sound,  or  other  external  influence.  Finally,  a  most  im- 
portant fact  about  cerebral  reaction  is  the  indefinitely 
long  time  that  may  elapse  between  the  stimulus  and  the 
expressed  result.  A  condition  which  operated  on  the 
cortex  at  a  certain  time  may  seem  to  have  been  wholly 
ineffective,  but  it  may  modify  the  reaction  to  another 
stimulus  much  later.  A  bit  of  information  which  was 
read  with  indifference  and  apparently  forgotten  may 
shape  one's  course  of  conduct  in  a  future  emergency. 

It  is  held  by  some,  among  others  by  Morton  Prince,  that 
nothing  is  ever  forgotten.  Diflftculties  and  limitations  in 
the  way  of  recollecting  must  be  admitted,  but  it  remains 
probable  that  every  impression  made  upon  the  cortical 
organization  is  a  permanent  one.  Every  stimulus  modi- 
fies the  cortical  structure  in  some  degree,  and  it  is  forever 
unlike  what  it  would  have  been  if  that  stimulus  had  never 
been  applied  to  the  receptors.  The  psychologic  corollary 
is  that  we  are  likely  to  recall  under  particular  conditions 
anything  that  we  have  ever  heard,  read,  or  witnessed. 
The  difficulty  is  to  control  the  ''conditions"  referred  to. 
The  images  from  the  distant  past,  often  of  very  trivial 


138      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

objects  and  situations,  which  arise  in  our  dreams  favor  the 
beUef  of  Prince. 

We  must  now  attempt  to  connect  the  view  that  the 
cortical  reactions  are  essentially  reflexes,  though  often 
delayed  and  modified  by  many  factors,  with  mod(M-n 
doctrines  of  localization.  A  brief  discussion  of  the  "motor 
areas"  will  be  in  order.  It  was  discovered  in  1870  by 
German  investigators  that  electric  stinmlation  applied 
to  the  corebral  cortex  of  the  dog  at  certain,  definite  places 


Fig.  22. — The  human  cerpbrum  is  sketched  from  the  left  side. 
The  crosses  are  sprinkled  on  the  area  from  wliicli  the  muscles  of  the 
right  half  of  the  body  appear  to  be  governed.  This  area  extends  out 
of  sight  over  the  top  of  the  brain  and  dips  into  the  fissure  between 
the  two  hemispheres. 


calls  into  play  the  muscles  of  the  body  in  a  manner  which 
can  be  predicted.  The  muscles  thrown  into  contraction 
are  for  the  most  part  on  the  opposite  side  of  the  body. 
In  the  ape  motor  areas  exist  in  the  same  sense:  excitation 
of  the  cortical  neurons  at  certain  spots  leads  regularly  to 
movements  made  by  corresponding  groups  of  muscles. 
It  is  known  that  the  same  representation  of  the  muscular 
system  in  mosaic  form  can  be  demonstrated  on  the  surface 
of  the  cerebrum  in  man  (Fig.  22).     These  areas  are  evi- 


THE    CEREBRUM  139 

dently  unlike  each  other  and  unlike  the  neighboring  areas 
from  which  electric  stimulation  elicits  no  visible  reaction. 
They  are  believed  to  contain  the  perikarya,  from  which 
motor  projection  fibers  extend  downward  to  make  synaptic 
connections  with  neurons  which  directly  innervate  the 
muscles. 

But  in  our  discussion  of  fatigue  we  have  insisted  that 
the  perikarya  at  the  origin  of  any  set  of  projection  fibers 
cannot  be  regarded  as  the  ultimate  source  of  the  impulses 
which  traverse  these  fibers.  By  losing  sight  of  this  fact 
many  writers  have  probably  made  too  much  of  the  cere- 
bral motor  areas.  They  have  been  spoken  of  as  though 
they  were  creative  in  function  or  as  though  they  were 
certainly  the  precise  spots  where  the  metaphj'sical  force 
impinged  upon  the  material  mechanism.  Loeb  protested 
against  such  naive  views  and  presented  the  alternative 
with  great  clearness  in  his  "Comparative  Physiology  of 
the  Brain." 

Activity  in  the  motor  areas  doubtless  precedes  most  of 
our  muscular  activity.  But  what  takes  place  in  the 
motor  areas  is  the  result  of  currents  arriving  within  their 
boundaries  from  other  parts  of  the  brain.  So  the  re- 
responsibility  is  shifted  to  these  other  regions,  and  from 
these  again  to  others.  The  true  fountain-head  is  not 
found  in  the  cerebrum  at  all,  but  in  the  receptors  of  the 
afferent  system  or  in  the  energies  of  the  external  world. 
When  this  is  said  we  merely  reiterate  the  statement  that 
the  type  of  nervous  action  is  the  reflex,  and  that  we  cannot 
make  an  exception  of  those  processes  which  are  directed 
through  the  cerebrum.  "Through"  rather  than  "by" 
is  the  preposition,  and  the  distinction  is  of  the  greatest 
importance. 

The  central  exchange  of  the  telephone  system  is  an 
impressive  example  of  intricate  mechanism,  but  it  is,  after 
all,  an  intermediate  point,  and  its  function  is  to  give  di- 
rection rather  than  to  originate  communications.  More 
damage  can  be  done  to  the  whole  system  by  destroying 
the  exchange  than  by  attacking  sniy  other  single  feature, 


140      THE    iNEKVOUS    SYSTEM    AND    ITS   COXSEUVATION 

but  it  is  eviileut  tliat  cuttiiifi;  all  the  wires  at  various 
places  would  have  the  same  crippling  etiect.  This  is  a 
fair  analogy  to  help  one  to  understand  the  present  con- 
ception of  the  cortical  centers.  They  are  not  believed  to 
originate  impulses,  excepting  as  impulses  come  to  them; 
their  peculiarity  is  found  in  the  fact  that  in  them  a  vast 
number  of  neural  arcs  of  correlated  function  are  brought 
so  close  together  as  to  be  readil.y  subjected  either  to 
stimulation  or  to  damage. 

This  may  be  maintained  as  well  for  other  areas  of  the 
brain  as  for  the  motor  regions.  For  example,  certain 
portions  of  the  cortex  at  the  back  of  the  cerebrum,  par- 
ticularly where  the  surface  of  each  hemisphere  is  infolded 
and  lies  against  the  surface  of  its  fellow,  are  held  to  be 
visual  centers.  It  is  reported  that  injury  to  these  fields 
impairs  the  usefulness  of  the  eyes  and,  if  sufficiently  ex- 
tensive, causes  complete  loss  of  sight.  These  are  regions 
which  visual  impulses  enter  after  having  been  relayed  by 
the  midbrain  structures,  and  they  are  regions  from  which 
impulses  are  normally  sent  away  to  other  parts  of  the 
brain  so  that  other  actions  may  be  modified  as  a  result  of 
the  inflow  from  the  eyes.  To  destroy  such  areas  (on  both 
sides)  is  to  destroy  useful  vision,  but  it  is  really  a  system 
of  pathways  which  has  been  interrupted  and  not  a  reposi- 
tory of  visual  impressions. 

If  we  reduce  all  the  activities  of  the  cerebrum  to  elabo- 
rated reflexes  and,  as  such,  demand  for  them  external 
causation,  immediate  or  past,  what  becomes  of  freedom 
of  the  will?  This  is  a  troublesome  and  unwelcome 
question  which  different  thinkers  have  answered  in 
different  fashion.  It  may  be  thought  to  lie  outside  the 
proper  sphere  of  the  physiologist,  but  it  confronts  him 
when  he  becomes  a  teacher  of  hygiene.  It  haunts  every 
man  of  science,  as  it  has  haunted  theologians  and  philos- 
ophers of  all  ages.  Many  have  been  brought  to  the  essen- 
tial position  of  Jonathan  Edwards,  which  was,  in  brief, 
the  view  that  we  are  free  to  do  what  we  will,  but  not  to 
will  what  we  shall  do.     Candid  scientists  often  admit 


THE    CEREBRUM  141 

with  Miinsterbergi  that  one  must  alternate  between  two 
views  without  seeking  to  reconcile  them;  as  an  investigator 
one  must  look  for  material  causes,  but  for  the  sake  of 
moral  power  and  conviction  one  must  hold  fast  the  behef 
in  free  agency,  which  has  always  commended  itself  to 
the  men  who  have  done  most  for  the  world. 

Another  assertion  of  Miinsterberg  may  be  quoted  at 
this  point.  Many  writers  constantly  refer  to  the  "sub- 
conscious mind"  in  their  discussions  of  brain  activity. 
Is  it  not  better,  asks  the  psychologist,  to  reserve  the 
word  "mind"  for  that  which  is  conscious?  Phyvsiologists 
will  certainly  agree  to  this;  most  of  the  action  of  the  ner- 
vous system  is  subconscious,  but  nothing  would  seem  to 
be  gained  by  caUing  such  action  mental. 

1  "Psychotherapy,"  Moffat,  Yard  &  Co.,  New  York,  1909,  chap.  iii. 


CHAPTER  XI 

THE    CEREBRUM    AND    HUMAN    DEVELOPMENT 

The  motor  areas  of  the  cerebral  cortex  were  first 
demonstrated  by  experiments  upon  the  dog,  and  hiter 
shown  to  exist  in  the  brain  of  the  ape.  In  the  cerebrum 
of  man  they  are  known  to  occupy  a  similar  position  and 
to  have  the  same  properties.  This  is  to  say,  that  when 
points  within  them  are  electrically  excited,  movements 
result,  and  chiefly  on  the  part  of  muscles  on  the  opposite 
side  of  the  body.  The  subdivisions  of  the  general  motor 
area  are  permanent  in  the  sense  that  the  same  group  of 
muscles  always  responds  when  a  selected  spot  is  stimu- 
lated. The  areas  are  better  developed  in  man  than  in 
the  ape,  and  better  in  the  ape  than  in  the  dog  or  the  cat. 
This  is  in  harmony  with  the  fact  that  muscular  move- 
ments in  the  lower  animals  are  largely  governed  by  means 
of  reflex  arcs  that  do  not  ascend  into  the  cerebrum.  It 
follows  naturally  that  injury  to  the  motor  regions  in  man 
results  in  irreparable  interference  with  muscular  move- 
ments, though  we  have  seen  that  in  the  dog  the  entire 
cerebrum  may  be  destroyed  and  the  power  of  locomotion 
remain. 

It  may  seem  strange  that  the  existence  of  motor  areas 
should  have  been  proved  for  the  human  brain.  The  facts 
are  as  follows:  In  certain  types  of  epilepsy  it  was  noted 
long  ago  that  each  attack  is  ushered  in  by  an  invariable 
initial  movement.  The  closing  of  one  fist  or  the  drawing 
of  the  lips  toward  one  side  may  give  a  reliable  warning 
of  the  approaching  convulsion.  When  it  became  known 
that  definite  motor  areas  occur  in  the  brain  of  the  ape, 
the  surgeons  conjectured  that  homologous  areas  might 
be  assumed  to  have  their  place  in  the  brain  of  man,  and 

142 


THE    CEREBRUM    AND    HUMAN    DEVELOPMENT       143 

that  such  cases  of  epilepsy  as  those  referred  to  might  be 
due  to  mechanical  sources  of  irritation  acting  at  the 
subcenter  for  that  part  which  was  first  moved  at  each 
seizure.  In  the  course  of  time  operations  for  the  relief 
of  epilepsy  were  undertaken.  Acting  on  the  theory  that 
the  brain  of  man  is  similar  in  its  large  features  to  that  of 
the  ape,  the  surgeons  plotted  in  advance  the  presumptive 
position  of  the  motor  areas  in  general,  and  of  that  one  in 
particular  which  was  thought  to  be  subject  to  abnormal 
stimulation.  In  very  many  cases  the  spot  of  cortex  which 
they  proceeded  to  expose  was  found  to  be  under  obvious 
pressure  or  otherwise  affected  by  pathologic  conditions. 
A  measure  of  relief  from  the  epileptic  symptoms  followed 
such  operations,  though  complete  cures  were  not  usual. 

When  the  surface  of  the  human  brain  has  been  laid  bare 
for  these  operations  it  has  been  possible  to  apply  weak 
electric  stimuli  to  its  convolutions,  and  the  movements 
made  by  the  skeletal  muscles  of  the  subject  have  justified 
the  belief  that  the  organization  here  is,  indeed,  closely 
similar  to  that  in  the  ape.  Microscopic  study  supports 
this  view.  A  conspicuous  system  of  projection  fibers  can 
be  traced  from  the  supposed  motor  regions  inward  through 
the  internal  white  matter  of  the  cerebrum  and  thence 
down  the  brain-stem.  In  the  medulla  the  great  majority 
of  these  fibers  cross  the  midline  and  pass  down  the  cord  on 
the  side  opposite  to  that  of  their  origin.  They  form 
synapses  with  motor  cells  of  the  cord  and  so  command 
the  muscles. 

The  impression  prevails  that  a  portion  of  the  cortex  just 
posterior  to  the  motor  areas  has  as  a  distinctive  property 
the  reception  of  afferent  impulses  from  various  parts  of  the 
body.  It  must  be  remembered  that .  incoming  impulses 
from  without  the  central  nervous  system  never  find  an 
uninterrupted  path  to  this  level;  the  original  neurons  do 
not  pass  above  the  medulla,  if,  as  a  matter  of  fact,  they 
extend  so  far.  It  is  by  synaptic  relays  that  transmission  to 
the  cerebral  cortex  is  secured.  If  we  adopt  the  usual 
conception  of  the  cortical  centers,  these  areas  of  reception 


144      THE    NERVOUS    SYSTEM    AND    ITS    CONSKI{VATION 

are  significant  cliiefly  as  they  forward  impulses  to  other 
places.  As  Loel)  has  said,  this  is  a  dynamic  rather  than  a 
static  form  of  localization.  As  this  is  true  of  the  sensory 
impulses  from  the  body  at  large,  so  it  is  prol)ably  true  for 
the  more  highly  developed  sense  organs,  such  as  the  eye 
and  the  ear. 

In  the  brain  of  man,  as  in  that  of  the  monkey,  the  visual 
impulses — or,  rather,  the  impulses  of  visual  origin — are 
projected  to  the  hinder  part  of  the  cortex  and,  chiefly,  to 
the  area  called  the  cuneus.  This  is  a  distinctly  marked 
triangle  set  off  by  fissures  upon  the  surface  of  the  occipital 
lobe  which  confronts  the  corresponding  area  of  the  opposite 
side.  As  the  relation  between  the  cerebrum  and  the  skele- 
tal muscles  is  so  largely  a  crossed  or  contralateral  one,  the 
inference  might  easily  he  drawn  that  the  impulses  from 
the  right  eye  would  be  found  to  arrive  in  the  cortex  of  the 
left  side,  but  in  the  human  organism  this  is  not  so.  The 
relationship  is  less  simple.  Approximately  half  of  each 
eye  has  efficient  connections  with  the  cerebral  cortex  on 
the  same  side.  An  able  teacher  has  Hkened  the  situation 
to  that  of  a  driver  with  a  pair  of  horses.  His  right  hand 
holds  the  reins  which  connect  with  the  right  side  of  ])oth 
the  bits;  his  left  hand  is  joined  through  the  reins  with  the 
left  side  of  both.  Carrying  this  comparison  over  to  the 
visual  apparatus,  it  reads  like  this:  the  right  occipital 
cortex  is  functionally  related  with  the  right  halves  of 
both  the  retinae;  the  left  cortex,  with  the  left  halves. 

The  general  statement  just  made  requires  a  quaUfica- 
tion  in  view  of  a  very  interesting  fact.  There  is  in  the 
center  of  each  retina  a  restricted  region,  the  fovea,  which 
has  superior  visual  possibiUties.  (When  we  speak  of  fix- 
ing the  eye  on  an  object  we  mean  fixing  the  image  of  the 
object  upon  the  fovea.)  This  part  of  the  retina  is  beheved 
to  have  a  double  representation  on  the  cortex — both 
eyes  projecting  impulses  to  both  sides  of  the  brain. 
Thus,  no  injury  confined  to  one  side  of  the  brain  can  be 
expected  to  destroy  the  use  of  either  fovea.  It  can  blot 
out  nearly,  but  not  quite,  half  of  the  field  of  vision.     The 


THE    CEREBRUM    AND    HUMAN    DEVELOPMENT       145 

"central  vision,"  which  is  of  the  foremost  importance,  is 
bound  to  survive,  thanks  to  the  reduphcated  projection  in 
the  cortex. 

The  auditory  path  leads  first  to  the  medulla  and  thence, 
by  repeated  relays,  to  the  cerebrum.  The  best  marked 
projection  of  the  impulses  from  the  organ  of  hearing  is 


Fig.  23. — The  upper  figure  represents  the  left  hemisphere  from 
outside,  that  is,  from  the  left.  The  lower  figure  shows  the  internal 
or  mesial  aspect  of  the  right  hemisphere,  that  is,  the  right  hemisphere 
from  the  left  side.  Areas  usually  claimed  to  possess  special  relations 
are  marked  as  follows:  H,  hearing;  V,  vision;  Sm,  smell;  Sp,  speech. 

upon  the  cortex  of  the  temporal  lobe,  and  damage  to  this 
part  has  often  caused  deafness.  The  effect  is  to  impair 
more  considerably  the  reactions  from  the  opposite  ear, 
though  some  hmitation  is  imposed  upon  the  usefulness  of 
the  ear  of  the  same  side.  An  area  for  the  reception  of  im- 
pulses of  olfactory  origin  is  said  to  be  well  set  off.     It 

10 


l4(3      THE    NERVOUS    SYSTKM    A\D    ITS    CONSEin'ATION 

is  not  far  fruin  tlic  place  of  entrance  of  the  olfactory  fibers 
into  the  lower  surface  of  the  cerebral  mass  (Fig.  23). 

While  these  several  regions  of  the  cerebral  cortex  have 
been  mentioned  with  especial  reference  to  man,  Uttle  has 
been  said  so  far  that  would  not  apply  as  well  to  the  more 
highly  developed  animals.  It  is  a  question  of  great 
moment  whether  there  are  to  be  discovered  in  the  brain 
clear  and  well-localized  signs  of  human  eminence.  As  to 
the  answer  to  this  question,  there  is,  unhappily,  a  great 
deal  of  disagreement.  Fifteen  or  twenty  years  ago  the 
average  writer  would  have  felt  warranted  in  more  posi- 
tive assertions  than  it  is  usual  to  make  at  the  present 
time.  But  in  spite  of  conservative  tendencies  there 
are  some  teachings  which  retain  weight  for  most  physiol- 
ogists. The  first  and  most  sweeping  of  these  is  that  the 
developments  in  brain  organization  which  correspond  with 
intellectual  advance  are  one  sided  rather  than  symmetric. 

Early  metaphysicians,  like  Descartes,  were  troubled  by 
the  dual  form  of  the  brain.  So  long  as  they  emphasized 
its  connection  with  mind  instead  of  body,  such  a  double 
character  seemed  unreasonable.  As  soon  as  men  began 
to  view  the  brain  in  its  relations  with  the  paired  muscles 
and  sense  organs  of  the  body,  its  division  into  right  and 
left  halves  appeared  justified.  But  the  desire  to  find  in 
it  some  basis  for  a  unity  closer  than  that  of  two  equal 
and  cooperating  halves  was  bound  to  rise  again.  Most 
investigators  think  that  it  has  been  fulfilled  in  the  prob- 
able fact  that  one  of  the  hemispheres  is  dominant  and  the 
other  subordinate,  so  far  as  truly  intelligent  activities  are 
concerned. 

Most  people  are  right  handed.  This  means  that  the 
motor  area  on  the  left  side  of  the  brain  has  a  superior 
organization.  By  this  we  now  understand  a  superior 
richness  of  connections,  association  tics  with  other  regions 
of  the  hemisphere.  The  majority  of  physiologists  will 
probably  go  so  far  as  to  say  that  the  machinery  of  intel- 
ligence lies  more  in  the  left  than  in  the  right  half  of  the 
cerel^rum  in  right-handed  individuals.     It  is  supposed  that 


THE    CEREBRUM    AND   HUMAN    DEVELOl'MENT       147 

in  the  left  handed  the  balance  is  reversed :  the  right  hemi- 
sphere is  the  dominant  one.  The  most  interesting  claims 
made  in  support  of  such  views  have  reference  to  the  repre- 
sentation of  language  in  the  human  brain. 

The  brain  of  an  ilUterate  man  is  organized  in  such  a  way 
that  oral  expression  of  thought  is  possible  and  that  the 
speech  of  others  is  comprehended.  The  educated  man 
has,  in  addition,  an  equipment  that  makes  possible  the 
expression  of  thought  in  writing  and  its  appreciation 
through  reading.  The  answering  of  a  question  is  an  act 
of  the  reflex  type,  but  one  which  requires  for  its  execution 
the  fullest  development  of  brain  paths.  The  manner  of 
its  accomplishment  must  depend  upon  innumerable  past 
events.  The  destruction  of  certain  connections  might  be 
expected  to  render  it  impossible  to  reply  to  the  question. 
This  is  a  state  of  things  quite  often  realized.  Brain  disease 
is  often  signahzed  by  disorders  in  the  field  of  language. 
.Such  disorders  are  not  sharply  distinguished  one  from 
another,  but  the  attempt  is  often  made  to  classify  them 
under  several  heads.  In  general,  it  may  be  said  that  the 
power  to  understand  and  to  reproduce  language  is  asso- 
ciated with  connections  made  through  the  cortex  of  the 
left  hemisphere  excepting  in  left-handed  subjects. 

Long  ago  it  was  noted  that  in  cases  where  there  had  been 
loss  of  intelligent  speech  during  life  a  certain  limited  area 
in  the  left  frontal  region  was  often  found  abnormal  on 
postmortem  examination.  This  area  became  known  as 
the  speech  center,  and  the  interference  with  speech  re- 
sulting from  its  impairment  was  named  motor  aphasia. 
The  reputed  center  is  probably  a  place  within  which  many 
of  the  arcs  which  are  necessary  for  vocal  expression  of  ideas 
are  brought  close  together.  Motor  aphasia  is  not  an 
actual  paralysis  of  the  muscle  groups  required  for  speech. 
The  use  of  the  same  parts  for  other  purposes,  such  as 
swallowing,  coughing,  and  even  for  voice  production, 
when  this  is  not  strictly  intelligent,  may  remain  quite 
unimpaired. 

The  distinction  between  the  intelligent  and  the  merely 


148      THE    NERVOUS    SYSTEM    AxND    ITS    CONSERVATION 

mechanical  employment  of  the  vocal  organs  may  be  illus- 
trated b}^  one  of  the  many  curious  stories  told  of  persons 
witii  aphasia.  A  man  who  suffered  from  an  injury  to  the 
region  assumed  to  bear  this  important  relation  to  language 
lost  all  command  of  speech  save  that  he  still  swore  on 
occasions.  This  seriocomic  state  of  affairs  is  not  difficult 
to  explain.  Habitual  profanity  is  scarcely  a  genuine  form 
of  speech;  the  few  words  used  are  repeated  under  the 
most  varied  circumstances  with  no  specific  appropriate- 
ness. They  come  to  be  little  more  than  animal  outcries. 
As  such  they  might  be  expected  to  survive  the  wreck  of 
the  organization  which  has  for  its  duty  the  rendering  of 
thought  in  correctly  chosen  words.  Thoughtful  cursing 
would  be  an  appalling  performance. 

Motor  aphasias  may  differ  in  degree  throughout  all 
grades  from  a  mere  limitation  in  vocabulary  to  absolute 
abolition  of  speech.  The  individual  characteristics  of  the 
cases  are  often  of  strange  interest.  A  number  of  them 
are  cited  in  a  fascinating  way  by  Thomson  in  his  delight- 
ful book,  "Brain  and  Personality. "^  We  may  refer  to  one 
shrewd  deduction  of  this  practitioner  which  seems  highly 
suggestive.  In  a  family  of  his  acquaintance  there  were 
several  children.  One  of  them  and  only  one  showed  a 
marked  preference  for  using  the  left  hand  in  the  first 
and  second  years.  A  rather  severe  struggle  followed,  the 
parents  and  attendants  seeTcing  to  make  the  child  right 
handed.  Its  initial  tendency  was  at  length  overruled 
and  it  grew  up  like  its  brothers  and  sisters.  But  in  one 
respect  its  history  was  contrasted  with  theirs :  all  the  others 
talked  at  an  early  age,  while  this  child  was  distinctly 
backward. 

Thomson's  explanation  is  an  attractive  one.  He  sug- 
gests that  in  the  brain  of  the  child  who  showed  the  dis- 
position to  use  the  left  hand  rather  than  the  right  the 
organization  of  the  right  hemisphere  had  begun  to  forge 
ahead  of  that  of  the  left.  If  there  had  been  no  interference 
from  without,  the  pathways  employed  in  the  use  of  lan- 
1  Dodd,  Mead  &  Co.,  New  York,  1907. 


THE    CEREBRUM    AND    HUMAN    DEVELOPMENT       149 

guage  would  have  been  opened  in  the  right  hemisphere  also. 
When  the  left  hemisphere  was  forced  to  provide  the 
nervous  government  for  the  skilled  hand  the  mechanisms 
related  to  language  had  likewise  to  be  furnished  by  that 
side  of  the  cerebrum.  Time  was  lost  when  the  original 
foundations  in  the  right  hemisphere  were  abandoned  in 
favor  of  new  ones  which  had  to  be  constructed  in  the  left. 

When  the  command  of  spoken  language  suffers  it  is 
commonly  observed  that  the  subject  shows  some  loss  of 
general  intelHgence  and  of  the  power  to  read  and  write. 
But  there  have  been  many  cases  in  which  one  or  another 
of  these  specific  accompHshments  has  been  more  or  less 
completely  abolished  without  much  impairment  of  the 
remaining  functions.  So  we  read  of  the  loss  of  the  ability 
to  write  consequent  on  damage  to  a  region  just  above  the 
speech  center  as  usually  indicated.  The  writing  center,  if 
it  has  as  definite  an  existence  in  space  as  has  been  claimed 
,  for  it,  is  near  the  motor  area  for  the  trained  hand  and  may 
be  thought  of  as  a  special  extension  of  that  area. 

Sometimes  the  power  to  read  is  lost,  though  the  victim 
is  not  blind.  The  letters  are  seen  clearty  enough,  but  do 
not  rouse  the  associations  which  they  had  previously 
acquired.  It  is  a  set-back  in  education — a  return  to  the 
condition  of  the  child  whose  eyes  are  keen,  but  who  has 
not  learned  to  read.  Since  reading  is  a  specially  devel- 
oped function  of  vision,  it  is  not  strange  that  a  state  like 
this  has  often  attended  injury  to  the  hinder  part  of  the 
cerebrum  on  the  left  side  and  outside  the  general  visual 
region.  Destructive  processes  near  but  not  covering  the 
supposed  auditory  area  of  the  left  temporal  lobe  have 
sometimes  led  to  a  condition  described  as  ''word  deafness," 
sounds  being  distinctly  heard,  but  words  no  longer  serving 
to  convey  their  old  meanings.  The  experience  is  probably 
just  that  of  listening  to  an  unfamiliar  foreign  language. 

The  integral  existence  of  four  centers  for  language, 
that  is,  for  vocal  speech,  writing,  reading,  and  the  transla- 
tion of  words  spoken  by  others,  is  not  so  confidently 
maintained  as  it  was  a  few  years  ago.     If  the  true  con- 


150      THE    XERVOrS    SYSTEM    AND    ITS    CONSEUVATIO.V 

cc'ptioii  of  a  "('('ntci"  is  merely  tliai  it  is  a  place  where  a 
large  number  of  paths  related  in  function  He  close  together 
in  the  cortex,  we  shall  expect  to  find  that  none  of  the  uses 
of  language  can  be  cut  off  by  local  brain  injury  without 
nnlucing  to  some  extent  the  other  powers.  This  has  been 
said  to  be  observed,  at  least  as  a  rule. 

The  attempt  has  been  made  to  ascertain  whether  the 
apparent  superiority  of  the  left  cortex  can  be  demon- 
strated with  the  microscope.  Melius,  of  Johns  Hopkins, 
has  recently  reported  that  sections  made  from  the  sup- 
posed speech  center  in  a  human  brain  and  from  the  corre- 
sponding area  on  the  opposite  side  have  proved  to  be 
markedly  unlike.  The  cortical  layer  on  the  left  side  was 
nmch  thicker  than  that  in  the  specimen  used  for  com- 
parison. The  greater  thickness  seemed  to  denote  a  more 
extensive  development  of  dendritic  processes  in  the  part 
held  to  have  the  special  functions  to  fulfil.  But  these 
facts  were  not  presented  without  a  word  of  caution.  The 
same  investigator  compared  sections  of  cortex  from  the 
Ijrain  of  a  highly  educated  man  and  others  from  homol- 
ogous localities  in  the  brain  of  an  ignorant  Austrian 
peasant.  The  drawings  made  showed  a  decidedly  more 
intricate  organization  in  one  case  than  in  the  other,  but, 
contrary  to  the  expectation  of  every  one,  the  more  impos- 
ing appearance  was  that  of  the  uneducated  brain! 

No  modern  advocate  of  cerebral  localization  has  ap- 
proached the  old  phrenologic  precision  in  denoting  the 
functions  of  all  regions.  Large  portions  remain  without 
designation  other  than  that  of  "association  areas." 
Through  them,  by  few  or  many  relays,  we  suppose  that 
the  connections  are  made  which  determine  the  reactions 
which  shall  occur  under  all  circumstances.  Histologists 
have  made  the  general  statement  that  only  the  areas 
which  are  definitely  classed  as  motor  or  sensory  have 
projection  fibers  mediating  between  them  and  lower 
levels  of  the  nervous  system.  Beyond  the  boundaries 
cf  the  areas  immediately  concerned  with  the  delivery 
or   the   reception   of  impulses   traveling   to   or  from  the 


THIC    CEREBRUM    AND    HUMAN    DEVELOPMENT       151 

various  parts  of  the  body  are  extensive  regions  linked 
with  them  and  with  each  other  by  paths  composed  of 
"association  fibers."  Hence  the  association  areas  seem 
to  rank  above  the  others  in  the  cerebral  organization, 
being  one  remove  farther  from  the  receptors  and  effectors 
in  which  the  nervous  system  begins  and  ends. 

Presumably  it  is  the  association  areas  which  register 
most  fully  the  details  of  the  individual  history,  and  so 
come  to  be  in  some  sense  the  protoplasmic  record  of 
experience  and  of  character.  But  the  representation  is 
diffuse,  and  the  attempt  to  attribute  a  specific  share  to 
this  or  that  fraction  of  the  whole  has  not  been  very  suc- 
cessful. The  most  attractive  description  of  the  associa- 
tion areas  and  the  possible  distribution  of  their  work  is 
that  of  Flechsig.^  He  has  suggested  that  the  association 
area  which  lies  mainly  in  the  parietal  lobe  is  particularly 
engaged  in  correlating  the  impulses  received  in  the  primary 
sensory  areas  around  it.  The  great  frontal  area  which  is 
more  distinctly  withdrawn  from  the  sensory  stations, 
but  which  adjoins  the  motor  Centers,  may  be  supposed 
to  transmit  impulses  to  the  cell  groups  controlling  move- 
ment. The  influence  exerted  through  the  frontal  region  is 
assumed  to  be  largely  of  an  inhibitory  character. 

If  the  views  advanced  by  Flechsig  were  quite  correct, 
it  should  be  possible  to  find  confirmatory  evidence  in  the 
nature  of  insanity  when  induced  by  local  brain  disease. 
Degeneration  in  the  parietal  region  might  be  expected  to 
cause  dulness,  apathy,  and  inaction  because  the  power 
to  appreciate  the  significance  of  things  seen,  heard,  and 
felt  would  be  impaired.  On  the  other  hand,  damage 
to  the  frontal  convolutions  might  be  expected  to  lead  to 
erratic,  ill-regulated  conduct,  perhaps  to  violence  or  de- 
pravity. The  facts  are  not  entirely  in  accord  with  the 
theory,  but  many  individual  cases  are  so,  and  it  is  pos- 
sible that  all  can  be  explained  under  its  broad  provi- 
sions. 

CUnical  observations  constantly  impress  upon  us  the 
1  Gehirn  und  Seele,  Leipzig,  1896. 


1d2    the  nervous  system  and  its  conservation 

danger  of  being  too  dogmatic  with  regard  to  the  local 
functions  of  the  brain.  We  are  reminded  of  this  when  we 
consider  the  extremely  unequal  results  of  various  brain 
injuries.  Sometimes  profound  effects  follow  what  seems 
quite  limited  destruction;  sometimes  extensive  lesions 
leave  no  noticeable  deficiency.  Gunshot  wounds  of  the 
brain  are  usually  fatal,  but  they  are  not  always  so,  and  it 
is  to  be  remembered  that  a  bullet  penetrating  the  brain 
substance  works  havoc  with  the  structure  far  beyond  its 
own  path,  displacing  the  tissue  and  producing  pressure 
in  distant  places.  There  have  been  extraordinary  cases 
of  immunity  from  serious  consequences  when  the  brain 
has  suffered  gross  harm.  Of  those  carefully  recorded, 
none  is  more  remarkable  than  that  of  Phineas  Gage.^ 

The  accident  which  befell  this  man  occurred  in  the 
year  1848,  when  the  Rutland  Railroad  was  under  con- 
struction in  southern  Vermont.  It  happened  near  the 
village  of  Cavendish,  where  a  rock  cut  was  being  made. 
Gage,  who  was  one  of  the  workmen,  was  tamping  a  charge 
of  blasting-powder  in  a  deep  hole  which  had  been  drilled 
into  the  ledge.  The  explosive  was  ignited  and  the  massive 
iron  bar  was  torn  from  the  hands  of  Gage  and  driven 
through  his  skull.  It  entered  his  left  cheek  and  went  out 
through  the  top  of  his  head,  having  pushed  before  it  a 
cjdindric  body  of  gray  and  white  matter  from  the  left 
hemisphere.  The  victim  did  not  even  lose  conscious- 
ness. He  survived  for  twenty  years,  and  it  is  not  known 
that  he  showed  any  abnormalities  excepting  blindness  in 
the  left  eye.  This  was  due  to  the  clipping  of  the  optic 
nerve  on  that  side  and  not  to  any  cerebral  damage. 

^  See  the  statement  of  Gage's  physician,  Williams,  in  the  guide- 
book of  the  Rutland  Railroad,  "The  Heart  of  the  Green  Moun- 
tains," 1S97. 


CHAPTER  XII 

THE   CEREBRUM   AND   THE  LIFE   OF  THE 
INDIVIDUAL 

In  some  of  the  tissues  of  the  body  there  is  a  constant 
formation  of  new  cells  at  every  period  of  life.  This  is  true 
of  the  skin,  and  is  nowhere  more  evident  than  in  the  case 
of  its  outgrowths,  the  nails  and  the  hair.  In  other  tissues 
there  is  no  addition  to  the  original  number  of  the  cellular 
units.  It  has  been  stated  in  another  connection  (Chapter 
VIII)  that  no  multiplication  of  the  units  occurs  in  the 
skeletal  muscles,  though  there  may  be  an  increase  in  the 
diameter  of  the  fibers.  It  is  a  most  significant  fact  that 
in  the  nervous  system  the  maximum  number  of  the 
neurons  appears  to  be  attained  very  early,  and  hence  any 
later  change  will  mean  a  diminution.  The  great  ad- 
vances made  from  infancy  onward  to  maturity  are  not 
based  upon  any  corresponding  multiplication  of  the 
neurons.  They  are  accomplished  in  spite  of  a  stationary 
or  even  decreasing  number  of  these  elements,  and  must  be 
referred  to  the  formation  of  new  routes  of  communication 
among  them. 

It  has  been  said  that  the  limited  powers  of  the  nervous 
system  in  the  newborn  are  indicative  of  the  great  individual 
development  which  awaits  realization.  This  subject  may 
now  be  pursued  in  some  detail.  The  receptor  system  of  the 
infant  is  probably  complete.  On  the  effector  side  the 
muscles,  especially  those  of  the  legs,  have  yet  to  grow 
considerably  to  sustain  a  proper  proportion  to  the  total 
mass  of  the  body,  but  they  are  fully  provided  with  efferent 
fibers  from  the  motor  cells  of  the  lower  order  in  the  cord 
and  brain.  The  department  of  the  nervous  system  which 
is  farthest  from  its  future  condition  is  the  intermediate 

153 


154      THE    NERVOUS    SYSTEM    AXD    ITS    CONSi:ilVATIOx\ 

portion,  the  adjustor  or  association  mechanism.  The  tics 
which  will  later  determine  the  responses  of  the  orj^anism  to 
all  manner  of  stimuli  have  mostly  to  be  established;  only 
a  few  are  congenital. 

The  light  which  enters  the  eyes  of  the  newborn  baby 
probably  produces  the  same  retinal  processes  which  it 
will  always  produce.  The  optic  paths  lie  ready  to  convey 
the  resulting-  impulses  to  the  brain.  The  lower  centers 
in  the  midbrain  and  thereabouts  may  be  traversed  by 
these  impulses  quite  as  they  will  be  in  adult  life,  and  the 
simpler  eye  reflexes,  such  as  winking  and  contraction  of 
the  pupil,  can  be  evoked.  But  the  radiation  of  the  im- 
pulses from  the  visual  centers  in  the  cerebral  hemispheres 
is  probably  insignificant.  A  few  months  later  the  child 
reaches  in  the  right  direction  to  grasp  objects  which  are 
brought  into  the  range  of  its  vision.  Physiologically 
speaking,  this  means  that  a  serviceable  bond  of  union 
has  been  established  between  the  receiving  station  for  the 
visual  impulses  and  the  area  from  which  the  motor  im- 
pulses take  their  departure  from  the  cerebrum.  When 
the  head  is  turned  toward  the  source  of  a  sound  it  seems 
reasonable  to  conclude  that  a  similar  connection  has  been 
secured  between  the  auditory  and  the  motor  regions. 

These  phj^siologic  gains  are  undoubtedly  accompanied 
by  mental  advances  of  a  parallel  sort.  In  a  passage  of 
great  literary  beauty  George  A.  Gordon^  has  sketched  the 
attainment  of  psychologic  correlation  between  sensations 
mediated  by  different  paths.  He  points  out  that  for  the 
baby  a  month  old  the  mother  is  represented  by  a  visual 
image,  a  voice,  and  a  comforting  touch.  The  three  sensa- 
tions have  nothing  in  common  save  the  fact  that  they 
are  welcome  to  the  infant  consciousness.  A  momentous 
step  is  taken  when  they  are  first  conceived  to  originate 
in  the  same  entity^ — a  "benign  power,"  as  the  author  cited 
has  expressed  it.  On  the  material  side  this  revelation  to 
the  mind  of  the  child  must  be  conditioned  by  the  opening 

'  "Ultimate  Conceptions  of  Faith,"  Houghton,  Mifflin  &  Co., 
Boston,  1903,  102-104. 


CEREBRUM    AND   THE    LIFE    OF   THE    INDIVIDUAL      155 

of  new  association  paths  in  the  cerebrum.  When,  after 
an  interval,  the  child  finds  a  name  for  the  mother  we  have 
evidence  of  an  additional  evolution  of  such  bonds. 

All  of  education,  from  infancy  to  the  fulness  of  develop- 
ment, is  of  this  same  type.  "Reaction  to  stimulation"  is 
the  term  which  covers  almost  all  which  the  organism  does, 
but  the  capacity  to  react  is  always  quaUfied  by  the  entire 
past  history  of  the  individual.  Every  incident  in  the 
course  of  life  has  left  its  impression.  The  formation  of 
habits  is  the  symbol  of  the  channeling  which  is  proceeding 
in  the  cortex.  This  fact  has  been  alluded  to  in  the  chapter 
on  Reflexes  and  it  may  now  be  enlarged  upon.  In  infancy 
a  very  few  repetitions  of  a  reaction  may  make  it  a  matter 
of  regular  recurrence  or,  in  other  words,  a  habit.  This  is 
partly  due,  we  may  suppose,  to  the  plastic  nature  of  the 
tissue  involved  and  partly  to  the  absence  of  paths  of  prior 
formation. 

When  the  word  "habit"  is  used,  the  connotation  is  likely 
to  be  a  disagreeable  one.  But  this  ought  not  to  be  so,  for 
it  is  the  power  to  form  habits  which  is  the  basis  of  human 
progress  and  efficiency.  If  it  were  not  possible  to  acquire 
the  ability  to  perform  many  acts  as  though  they  were 
reflexes,  making  no  demand  upon  the  attention,  we  should 
never  advance  far  in  our  individual  development.  If  the 
task  of  dressing  one's  self  remained  as  laborious  and  con- 
tinued to  require  the  same  thoughtful  planning  in  later 
life  as  in  the  days  of  childhood,  when  it  was  first  accom- 
plished, one  would  lose  just  so  much  time  and  strength 
which  is  actually  available  for  fresh  lines  of  thinking.  As 
each  necessary  act  becomes,  as  we  say,  second  nature,  the 
mind  is  released  for  new  conquests. 

The  late  William  James^  wrote  most  wisely  of  the  ad- 
vantages and  the  dangers  incident  to  our  habit-forming 
propensity.  It  was  his  suggestion  that  habits  can  be 
placed  in  three  classes:  those  which  are  clearly  the  best 
possible,  those  which  are  plainly  undesirable,  and  a  great 

1  "Psychology,  Briefer  Course,"  Henry  Holt  &  Co.,  New  York, 
1892,  chapter  on  Habit. 


150      THE    NERVOUS    SYSTEM    AND    ITS   CONSERVATION 

number  wliich  are  neither  to  be  particularly  commended 
nor  condemned.  The  habits  of  the  first  class  are  evidently 
to  be  cultivated  and  cherished,  while  those  of  the  second 
class  are  to  be  abandoned.  These  statements  are  plati- 
tudes, l)ut  the  teachino;  of  James  regardinfi;  the  ha))its 
which  are  neither  ^ood  nor  bad  is  worthy  of  cai'eful  con- 
sideration. His  contention  is  that  such  habits  are  to  be 
arbitrarily  changed  from  time  to  time;  not  that  the  new 
practices  are  any  more  hygienic  or  attractive  than  the  old, 
but  that  l)y  such  deliberate^  chang(\s  one  preserves  the  mas- 
tery of  the  situation  and  the  adaptability  of  the  nervous 
system  to  altered  conditions  which  the  future  may  bring. 

It  is  easy  to  find  opportunities  to  follow  this  suggestion. 
One  may  find  that  a  certain  phrase  is  being  used  repeatedly 
in  conversation  or  in  writing.  An  equivalent  phrase  may 
be  substituted;  this  is  combating  the  tendency  to  form  a 
rigid  habit.  A  certain  melody  may  run  in  the  head;  the 
act  of  cutting  short  its  continuance  and  causing  another 
air  to  take  its  place  or,  better  still,  silencing  the  subjective 
music  for  the  time  is  attended  with  an  agreeable  sense  of 
being  in  command  of  the  cerebral  activities.  James  has 
said  in  substance  that  one  should  note  what  one  is  in- 
clined to  do  and  then  do  something  else.  This  practice 
might  conceivably  be  overdone,  but  the  want  of  such 
initiative  and  the  passive  acceptance  of  all  the  minor  habits 
as  they  make  their  appearance  is  the  common  defect. 

It  is  not  too  much  to  claim  that  such  self-discipline  is  a 
postponement  of  old  age.  We  have  said  that  the  charac- 
teristic of  the  young  nervous  system  is  the  ease  with  which 
paths  may  be  opened  in  it.  The  nervous  system  in 
middle  life  has  many  well-defined  paths  which  are  em- 
ployed with  regularity  in  doing  the  daily  work  to  which 
the  subject  has  been  trained.  Changes  become  con- 
stantly more  difficult  and  are  made  more  reluctantly. 
Foster  has  said  that  in  old  age  the  brain  holds  a  record 
of  the  past  rather  than  a  promise  of  what  may  be  realized. 
Monotony  of  environment  and  consequent  uniformity  of 
reaction  are  factors  which  are  calculated  to  bring  on  pre- 


CEREBRUM   AND    THE    LIFE    OF  THE    INDIVIDUAL      157 

maturely  this  rigidity,  which  must  in  any  event  arrive  at 
last  unless  death  anticipates  it. 

The  hardening  of  the  arteries  in  later  years  is  an  im- 
portant and  widely  discussed  feature  of  the  senile  decline. 
Portending  the  day  when  "  the  pitcher  shall  be  broken 
at  the  fountain  or  the  wheel  broken  at  the  cistern,"  it 
is  a  material  type  of  the  invisible  change  in  the  constitu- 
tion of  the  central  gray  matter  which  gradually  limits  its 
capacity  to  respond  to  new  exactions.  Much  as  arterio- 
sclerosis can  be  postponed  by  temperance  in  eating  and 
drinking  and  by  a  wise  ordering  of  all  the  activities  of 
life,  so  the  loss  of  plasticity  in  the  cortical  organization 
can  be  delayed  by  the  same  temperate  conduct  with  the 
added  element  of  a  studied  variety  in  its  employment. 
It  seems  to  be  much  more  within  our  power  to  do  this 
than  to  prevent  the  inevitable  stiffening  of  the  crystalline 
lens  which  abolishes  the  accommodation  for  near  vision 
at  about  the  same  period  for  all  persons  with  normal 
eyes. 

It  will  be  gathered  from  what  has  been  said  that  if  the 
young  nervous  system  excels  the  older  one  in  its  capacity 
for  variation  in  reaction,  the  older  one  surpasses  the 
younger  in  its  confinement  of  its  energies  to  profitable 
channels.  It  is  the  more  economic  of  the  two.  This 
is  much  like  saying  that  it  has  the  greater  exercise  of  in- 
hibition. In  it,  wasteful  diversions  of  nerve-currents  to 
call  into  play  effectors  which  serve  no  useful  purpose  have 
become  reduced  to  a  minimum.  When  a  child  no  longer 
cries  when  matters  are  not  altogether  to  its  liking  and, 
instead,  seeks  compensations  in  each  situation,  it  has  sup- 
pressed or  inhibited  a  lower  type  of  reaction  in  favor  of  a 
higher  one.  The  progress  of  education  always  continues 
to  be  marked  by  such  substitutions. 

This  inhibition  of  primitive  reactions  by  others  based 
upon  complex  experiences  is  best  illustrated  by  the  human 
being,  but  is  not  wholly  wanting  in  the  most  intelligent 
of  the  lower  animals.  The  dog  that  endures  abuse  at  the 
hands  of  children  without  turning  upon  its  tormentors 


158      THE    NEK^■OLS    SYSTEM    AND    ITS    CONSERVATION 

exhibits  it  impres^sivcly.  We  feel  at  once  that  we  may  ae- 
knowledge  kinsliip  witli  a  creature  in  which  we  recognize 
the  beginnings  of  virtue  and  nobihty.  Translated  into 
physiologic  terms,  the  self-control  on  the  part  of  the  dog 
stands  for  the  existence  in  its  brain  of  countercurrents 
which  sta}^  the  execution  of  the  simpler  reflexes. 

As  men  and  women  we  find  ourselves  called  upon  not 
only  to  restrain  many  of  the  elementary  reactions,  but  also 
to  emplo}^  inhibition  with  reference  to  trains  of  thought. 
The  power  of  concentration  and  the  power  of  detach- 
ment are  nearly  related.  It  might  seem  that  they  were 
diametrically  opposed,  but  a  little  consideration  shows 
that  what  we  call  "concentration"  depends  on  the  banish- 
ment of  irrelevant  ideas,  and  one  who  can  do  this  will,  as 
a  rule,  have  the  ability  to  banish  the  central  as  well  as  the 
competing  thoughts  at  the  proper  time.  Those  who  have 
carried  the  most  crushing  responsibilities  for  long  periods 
and  rendered  the  greatest  services  to  mankind,  have  fre- 
quently been  those  in  whom  the  power  of  detachment 
from  their  cares  was  most  remarkable. 

Lincoln  furnishes  an  illustrious  example.  Those  who 
were  near  him  were  puzzled  and  sometimes  offended  by 
the  abandon  with  which  he  put  aside  perplexing  problems 
to  enjoy  humorous  books  or  amusing  plays.  It  was  not  so 
plain  to  them  as  it  appears  to  us  now  that  this  relaxation 
was  the  physical  and  mental  salvation  of  the  heavy-laden 
president.  Because  he  could  dismiss  the  pressing  questions 
when  it  was  no  longer  profitable  to  dwell  upon  them,  he 
could  return  with  renewed  strength  and  clarified  judgment 
to  his  task  a  little  later.  Stedman  saw  the  motive  and 
wrote  sympathetically  of 

"...  one  who,  longer  to  endure, 
Called  mirth  to  case  his  ceaseless  dole, 
Yet  kept  his  nobler  purpose  sure." 

The  same  fine  attainment  of  mastery  over  the  currents 
of  the  mental  life  lias  often  given  efficiency  to  those  who, 
unlike  Lincoln,  have  had  no  large  endowment  of  physical 


CEREBRUM    AND    THE    LIFE    OF    THE    INDIVIDUAL      15!) 

stamina.  This  was  doubtless  the  case  with  Darwin,  who 
could  not  long  pursue  any  single  interest,  but  had  to  find 
something  to  contrast  with  it  after  a  short  period  of  atten- 
tion. The  quantity  and  the  quality  of  the  work  which  he 
produced  in  spite  of  this  hmitation  convince  us  that  he 
must  have  had  in  equal  measure  the  power  to  appl}^  him- 
self in  the  most  concentrated  fashion  and  to  relax  with  the 
same  degree  of  success.  The  latter  achievement  is  probably 
found  to  coexist  with  the  ability  to  go  quickly  to  sleep. 

One  who  has  cultivated  the  ability  of  turning  resolutely 
from  one  line  of  thought  to  another  will  find  abundant 
opportunity  for  the  exercise  of  this  power  in  effacing  what 
is  disagreeable  in  favor  of  what  is  pleasant.  This  may  be 
true  either  of  memories  or  of  anticipations.  The  healthy 
mind — doubtless  correlated  with  a  healthy  brain — is 
greatly  aided  by  nature  in  banishing  distressing  recollec- 
tions. Psychologists  recognize  that  such  an  individual 
retains  in  his  thought  much  more  of  detail  and  of  vivid- 
ness when  the  experience  reviewed  is  pleasant  than  when 
it  is  the  reverse.  A  normal  person  should  be  able  to 
reproduce  with  but  little  diminution  the  feelings  which 
attended  joyous  and  uplifting  moments,  but  he  should 
find  that  pains  and  mortifications  recalled  from  his  past 
have  atrophied  to  colorless  abstractions.  The  opposite 
condition  is  particularly  deplorable  and  may  characterize 
the  neurasthenic. 

In  the  voluntary  control  of  thoughts  regarding  the  future 
we  must  recognize  a  matter  of  inestimable  importance. 
They  are  happy  who  can  systematically  magnify  the  ap- 
proaching good  and  disregard  the  impending  ill,  consider- 
ing it  only  to  the  extent  that  prudence  and  unselfishness 
require.  There  are  few  examples  more  inspiring  than  those 
which  we  owe  to  women  who  approach  terrifying  surgical 
ordeals  with  their  attention  steadfastly  fixed  on  other  con- 
cerns. We  do  right  to  pay  tribute  to  their  self-forgetful- 
ness,  but  it  may  fairly  be  added  that  their  splendid  disci- 
pline is  the  best  thing  possible  for  the  conservation  of 
their  own  resources  in  the  crisis. 


1(30      THE    NERVOUS   SYSTEM    AND    ITS   CONSERVATION 

Much  is  written  of  the  injury  to  general  health  which 
is  wrought  by  fear.  The  teaching  is  not  so  familiar  that 
there  are  many  people  who  need  to  limit  the  extent  to 
which  certain  entirely  happy  expectations  occupy  their 
minds.  Yet  this  may  fairly  be  claimed  when  dwelling  on  a 
distant  happiness  becomes  a  cause  of  discontent.  The 
homesick  college  student  knows  that  to  be  forever  reckon- 
ing the  daj's  that  remain  between  the  present  and  the 
tardily  coming  vacation  brings  more  of  depression  than  of 
stimulation.  It  is  better  to  emphasize  the  agreeable  con- 
ditions which  can  generally  be  discovered  close  at  hand. 

Monotony  in  occupation  and  association  must  be  held 
to  threaten  harm  to  the  nervous  system  and  so  to  the 
general  health.  We  see  the  consequences  in  remote 
country  districts,  where  each  person  sees  but  a  few  others, 
and  where  the  round  of  duties  to  be  performed  is  narrowly 
fixed  from  day  to  day  and  from  year  to  year.  Add  to  the 
wearing  uniformity  of  circumstance  the  anxiety  over  the 
slender  income  and  it  does  not  seem  strange  that  in  such 
localities  the  proportion  of  mental  derangement  is  high. 
In  many  a  weather-beaten  farmhouse  there  are  taciturn, 
desponding,  and  bigoted  people,  cherishing  bitter  grudges 
against  neighljors,  and  making  no  effort  to  maintain 
sociability  in  the  family  circle.  Every  such  man  or 
woman  is  a  witness  to  the  tragic  results  of  life  without 
wholesome  variety  in  contacts  and  interests. 

A  mind  well  stocked  ought  to  be  able  to  neutralize  in  a 
great  measure  the  drawbacks  of  such  surroundings,  though 
it  frequently  appears  that  the  man  of  ostensibly  high 
education  is  quite  dependent  upon  external  sources  of 
diversion.  Not  many  college  graduates  could  spend  a 
Avinter  on  a  poverty-stricken  farm  without  repining,  but  it 
may  be  asserted  that  the  success  of  an  academic  training 
may  be  measured  by  the  capacity  of  the  possessor  to  find 
contentment  independently  of  novel  stimuli.  It  is  too 
much  to  ask  that  he  shall  prefer  such  isolation;  formal 
education  is  naturally  a  preparation  for  further  develop- 
ment in  which  the  environment  should  bear  its  part. 


CEREBRUM   AND   THE    LIFE    OF   THE    INDIVIDUAL      1()1 

But  if  the  exigency  arises  it  should  be  possible  for  the 
trained  mind  to  meet  it  with  equanimity. 

A  store  of  happy  memories  and  generous  affections 
should  be  competent  to  provide  a  foil  to  the  depressing 
influence  of  monotonous  circumstances  for  a  time  at  least. 
Few  would  care  to  be  tested  long.  Books  have  been  one 
of  the  chief  resources  of  those  who  have  contended  without 
degenerating  against  the  tedium  and  pettiness  of  their 
lot.  Memorized  portions  of  the  best  literature  may  have 
a  share  in  saving  intellect  and  character  from  deteriora- 
tion. The  silent  or  audible  rehearsal  of  such  passages 
may  be  more  beneficial  than  a  concert  or  a  play.  No  one 
can  estimate  the  steadying  power  that  has  been  operative 
in  the  minds  of  our  ancestors  as  they  have  pondered  the 
words  of  the  Bible,  "the  ever-open  Thesaurus"  of  immortal 
truth  immortally  phrased. 

As  we  think  of  the  means  of  avoiding  a  dead  level  of  the 
mental  fife  and  the  value  in  it  of  reserve  capacity  for  in- 
hibition, the  topic  of  the  Sabbath  suggests  itself.  It  is 
easy  to  caricature  and  condemn  the  Sunday  of  the  Puri- 
tans. Many  of  the  restraints  which  it  imposed  may  ap- 
pear arbitrary  and  undesirable.  But  certain  great  bless- 
ings came  from  it  to  those  who  cordially  acquiesced  in  its 
conventions,  and  even  in  a  measure  to  those  who  con- 
formed more  grudgingly.  It  made  a  radical  break  with 
the  routine  of  the  other  six  days  and  it  encouraged  self- 
control  rather  than  self-indulgence.  The  ''Continental 
Sunday,"  toward  which  we  seem  to  be  moving,  has  too 
little  of  inhibition.  The  jaded  nervous  system,  by  a 
property  which  may  be  called  perverse,  demands  excite- 
ment, when  the  real  need  is  rest.  We  shall  find  in  this  fact 
the  key  to  much  that  we  have  to  discuss  in  a  later  chapter. 

The  student  who  refuses  to  let  his  studies  encroach 
upon  his  Sunday  is  not  likely  to  regret  his  course.  He  will 
find  a  zest  in  his  work  when  he  resumes  it  on  Monday  which 
is  the  direct  consequence  of  the  intermission.  The  relig- 
ious prohibition  of  our  fathers  may  not  be  well  founded, 
but  the  dictates  of  hygiene  may  be  made  to  take  its  place. 
11 


Ki'i      TlIK    XKKVOLS    SYSTEM    AND    JTS    ("OXSKRVATION 

Those  who  ck'iimr  a^auist  the  ijroscriptiun  t)f  religion  may 
ur^e  that  the  assigned  En<2;hsh  literature  or  history  is  intrin- 
sically finer  than  an}'  matter  likely  to  be  substituted  for  it; 
on  grounds  of  hygiene,  however,  a  change  is  to  be  desired. 
Some  experiments  recently  reported  from  the  Harvard 
Medical  School  support  this  claim  in  a  very  i)()sitive  waj'.' 

Daily  trials  were  made  upon  a  large  number  of  students 
to  determine  their  "sensory  threshold,"  meaning  in  this 
case  the  least  electric  shock  which  the}'  could  feel.  The 
stimulation  was  through  two  fingers  of  the  same  hand. 
When  all  the  results  were  averaged,  it  was  found  that  a 
diminution  of  irritability  was  registered  from  day  to  day 
as  the  week  passed,  until  on  Saturday  the  threshold  reached 
its  highest  level.  That  is  to  say,  it  took  a  stronger  shock 
to  attract  attention  on  that  da}^  than  on  any  other.  On 
Monday  the  threshold  was  down  again;  this  is  the  same 
as  saying  that  the  irritability  was  restored  to  the  highest 
pitch.  There  must  have  been  some  cumulative  fatigue 
from  one  day  to  the  next  which  was  not  offset  by  the  night's 
rest. 

The  students  in  this  group  probably  had  very  variable 
programs  for  Sunday.  But  it  could  be  said  of  all  of  them 
that  the  occupation  on  that  day  afforded  a  contrast  with 
that  which  filled  the  rest  of  the  week.  Perhaps  we  may 
find  in  facts  like  these  the  explanation  of  the  uniform 
seven-day  cycle  agreed  upon  by  so  many  races  and 
creeds.  Experience  may  have  shown  that  a  longer  period 
of  routine  leads  to  progressive  impairment  of  efficiency, 
while  economic  pressure  has  not  permitted  the  interrui)- 
tions  to  become  more  frequent.  Surprise  has  been  ex- 
pressed that  the  subjective  judgment  on  Monday  morning 
is  apt  to  be  that  the  condition  is  one  of  unusual  inertia 
rather  than  (jf  superior  capacity.  It  is  very  likely  true 
that  the  highest  irritability  does  not  correspond  with 
the  best  state  of  the  nervous  system  for  consecutive  work. 
The  subject  may  be  too  easily  distracted.    Hence,  it  may 

'  Martin,  Withington,  and  Putnam,  American  Journal  of  Physiol- 
ogy, 1914,  xxxiv,  97. 


CEREBRUM    AND    THE    LIFE   OB^    THE    INDIVIDUAL      163 

very  well  be  that  the  best  working  days  will  come  later  in 
the  week.  Still,  the  important  fact  remains  that  a  balance 
must  be  maintained,  and  the  seventh  day,  bringing  change 
if  not  rest,  is  invaluable. 

A  word  regarding  the  relation  of  attendance  on  church 
services  to  the  health  of  the  nervous  system  may  not  be  out 
of  place.  If  we  hold  to  the  principle  that  a  contrast  in 
thought  and  feeling  is  what  we  must  seek  to  secure  when 
we  turn  from  our  common,  necessary  interests  to  others 
which  invite  our  attention,  we  shall  find  that  much  can 
be  said  in  favor  of  the  formal  exercises  of  rehgion.  To 
cease  from  our  narrow  calculations,  our  competitive 
endeavors,  the  struggle  to  please  all  types  of  associates, 
and  to  contemplate  fixed  and  eternal  realities  is  to  alter 
as  completel}^  as  possible  the  currents  of  mental  life. 

It  may  be  said  in  this  connection  that  the  atmosphere 
of  very  many  churches  at  the  present  time  is  far  less  favor- 
able to  this  bitterly  needed  substitution  than  it  was 
twenty-five  years  ago.  When  a  church  becomes  a  socio- 
logic  forum  its  power  to  restore  the  jaded  individual  is 
obviously  lessened.  We  cannot  wholly  regret  the  heroic 
note  in  current  preaching,  the  insistent  call  to  social 
service  and  political  reform,  but  this  is  a  function  which  is 
shared  with  the  press  and  the  secular  platform,  while 
spiritual  renewal  is  the  preeminent  office  of  the  church  of 
Christ. 


CHAPTER  XIII 

EMOTION 

The  fact  has  been  emphasized  that  a  very  large  propor- 
tion of  the  action  of  the  nervous  system  proceeds  without 
clear  tokens  in  consciousness.  On  the  other  hand,  it  msiy 
be  urged  that  the  general  coloring  of  consciousness  is 
sjanptomatic  of  much  that  is  taking  place  in  all  depart- 
ments of  the  neural  mechanism  and,  indirectl}^,  of  many 
states  of  the  outlying  organs  which  we  cannot  attend  to  in 
an  analj'^tic  fashion.  Our  intense  feehngs  we  speak  of  as 
emotions,  and  it  is  generally  held  that  their  development 
depends  in  a  great  measure  upon  conditions  outside  the 
cerebrum  through  which  the  fusion  of  effects  is  brought 
about. 

The  doctrine  that  stirring  feelings  never  have  an  ade- 
quate force  in  the  mind  until  there  is  a  characteristic 
inflow  of  afferent  impulses  from  various  sources  to  give 
them  positiveness  is  known  as  the  James-Lange  theory. 
According  to  this  view  a  person  is  not  truly  angry  until 
his  muscles  have  assumed  a  certain  tension,  his  heart 
action  a  certain  rhythm,  and  his  blood-vessels  a  certain 
tonic  regulation.  He  does  not  realize  rage  until  his  facial 
expression  and  his  posture  combine  to  denote  it.  His 
emotion  is  interpreted  to  himself  by  the  same  signs  which 
make  it  known  to  others.  If  one  who  feels  angry  can 
inhibit  the  muscular  manifestations  and  relax  his  features 
he  will  experience  a  sense  of  ludicrous  impotence  and  dis- 
satisfaction, though  he  may  be  well  aware  that  the  occa- 
sion for  his  wrath  retains  its  full  validity. 

So  the  experience  of  grief  in  its  fulness  requires  the  sen- 
sations that  accompany  the  muscular  state  of  one  who  has 
given  way  to  sorrow  and  the  tingle  of  shedding  tears.    To 

164 


EMOTION  165 

know  the  meaning  of  fear,  one  must  blanch  and  cower. 
These  ideas  are  not  readily  accepted  by  the  student  who 
considers  them  for  the  first  time;  they  have  not  proved 
convincing  to  all  psychologists.  But  for  our  present  pur- 
pose it  does  not  much  matter  whether  the  bodily  accom- 
paniments of  emotional  states  precede  or  follow  the  feeling. 
What  concerns  us  is  the  plain  fact  that  they  attend  it 
closely.  They  are,  moreover,  in  proportion  to  its  intensity, 
and  it  is  important  to  realize  that  all  emotion  is  exercise 
and  often  of  a  strenuous  and  far-reaching  kind. 

People  who  criticize  athletic  sports  often  argue  some- 
what in  this  wise:  Here  are  20,000  people  idly  viewing  a 
contest  in  which  18  baseball  players  are  taking  part.  The 
proportion  of  the  idle  to  the  active  is  more  than  1000  to  1. 
Such  a  statement  does  but  scant  justice  to  the  facts.  There 
is  an  unsuspected  quantity  of  muscular  activity  among  the 
spectators  as  they  watch  the  game,  and  they  often  find 
that  they  have  earned  a  wholesome  fatigue  when  it  is 
ended.  As  they  bend  forward  or  rise  in  their  seats,  per- 
haps giving  vent  to  cheers  or  imprecations,  as  they  flush 
and  tremble,  now  holding  the  breath  and  now  gasping  or 
sighing  in  the  stress  of  their  feeling,  we  cannot  question 
that  both  the  skeletal  muscles  and  the  autonomic  system 
are  being  strongly  played  upon.  It  is  only  when  the  game 
is  very  one  sided  or  the  looker-on  is  very  blase  that  the 
hours  passed  in  the  grandstand  can  be  classed  as  idle. 

A  previous  reference  has  been  made  to  the  fact  that  in 
times  of  marked  excitement  the  adrenal  bodies  are  aroused 
to  unusual  activity  and  discharge  their  powerful  product, 
adrenalin,  into  the  circulation  at  a  more  rapid  rate  than 
normal.  The  demonstration  and  the  interpretation  of 
this  fact  we  owe  to  Cannon.  He  was  able  to  show  by  a 
delicate  test  that  adrenalin  makes  its  appearance  in  the 
blood  of  a  cat  when  the  animal  has  been  agitated  by  the 
sight  of  a  dog.  Additional  experiments  by  workers  in 
the  same  laboratory  have  shown  that  adrenalin  is  capable 
of  delaying  the  onset  of  muscular  fatigue.  This  is  accom- 
plished partly,  though  not  wholly,  by  its  acting  as  an  anti- 


IGO      THK    NKRVOrS    SYSTEM    AND    ITS    COXSKiaATlON' 

dote  to  the  fatigue  substances  at  the  end-plates.  Under 
the  same  concUtions  which  cause  the  discharge  of  adrenaUn 
there  is  hkely  to  be  a  notable  rise  in  the  sugar  of  the  blood 
above  the  usual  small  percentage. 

The  rise  of  the  sugar  may  be  sufficiently  marked  to  cause 
some  of  it  to  pass  into  the  urine.  This  feature  of  the 
emotional  state  has  been  noticed  in  human  ])eings.  Can- 
non found  that  such  an  escape  of  sugar  occurred  in  most 
of  the  members  of  the  Harvard  footl^all  squad  at  the  time 
of  the  game  with  Yale  in  1913.  This  was  true  of  the  sub- 
stitutes who  had  merely  expected  to  be  called  in  as  well 
as  of  the  active  players.  Moreover,  the  same  "emotional 
glycosuria"  was  found  to  be  common  among  the  specta- 
tors. It  is  probably  a  rather  frequent  reaction;  possibly 
the  excitement  of  being  examined  for  life  insurance  may 
sometimes  suffice  to  cause  it  and  to  mislead  the  physician 
who  detects  sugar  in  the  urine.  In  all  cases  it  is  the  glyco- 
gen or  animal  starch  in  the  liver  which  has  been  trans- 
formed to  furnish  the  sugar,  and  it  is  believed  that  the 
change  is  brought  about  by  the  influence  of  adrenalin  in 
the  blood. 

Cannon  has  shown  great  insight  in  his  explanation  of 
these  phenomena  of  emotion.  The  fundamental  fact  is 
that  emotions  are  experienced  b}^  the  lower  animals  and 
by  primitive  men  at  moments  when  vigorous  action  is  to 
follow.  Rage  is  the  prelude  to  conflict.  Fear  will  be  fol- 
lowed by  flight.  Sexual  passion  will  eventuate  in  sexual 
aggression.  Civilization  compKcates  the  order  of  reaction, 
and  inhibition  of  the  higher  type  represses  these  activities. 
The  physical  accompaniments  of  emotion  are  better  suited 
to  the  ancestral  than  to  the  modern  conditions.  The 
mobilization  of  sugar  appears  to  anticipate  a  demand  for 
fuel  on  the  part  of  the  skeletal  muscles.  The  extra  adre- 
nalin at  the  same  time  promotes  endurance. 

Very  recently  Cannon  and  his  co-workers  have  demon- 
strated another  and  a  curious  change  in  the  blood  after  an 
emotional  crisis.  This  is  a  distinct  reduction  in  the  time 
needed  for  coagulation.     The  clotting  of  the  blood  is  a 


EMOTION  167 

defensive  reaction  tending  to  check  hemorrhage  and,  in 
case  of  wounds,  to  increase  the  chance  of  survival.  Cannon 
suggests  that  emotion  is  experienced  when  wounds  are 
imminent,  and  so  a  purposive  character  can  be  discerned 
in  this  physical  change  as  in  the  others. 

If  emotion  is  exercise,  it  may  be  asserted  that  a  life 
poor  in  emotion  is  a  life  which  lacks  wholesome  stirrings 
in  both  the  neuromuscular  and  the  autonomic  realms. 
It  is  probably  true  that  people  who  have  had  a  humdrum 
existence  are  apt  to  be  wanting  in  endurance.  The 
country  cousin  on  a  visit  to  the  city  is  utterly  wearied  by 
days  of  sight-seeing  and  evenings  of  entertainment  in 
spite  of  keen  enjoyment  of  it  all.  It  has  often  been  ob- 
served that  volunteers  from  .the  city  are  more  readily 
made  into  seasoned  and  hardy  soldiers  than  are  the  more 
formidable  looking  farmers.  A  measure  of  training  is 
inseparable  from  irregular  hours,  various  associates, 
changes  of  boarding-place,  and  the  more  harmless  dissi- 
pations of  the  city.  The  hurry,  the  noise,  and  the  glare, 
the  very  things  which  are  held  to  injure  the  nervous  sys- 
tem, harden  it  and  adapt  it  to  endure  new  forms  of  stimu- 
lation if  it  is  intrinsically  strong  enough  to  withstand 
them. 

At  the  same  time  it  is  easy  to  see  that  excess  in  emotion 
is  exhausting  to  all  the  physical  resources.  Most  people 
know  how  profound  is  the  weariness  which  succeeds  a 
severe  paroxysm  of  anger.  It  is  not  much  less  marked 
after  sudden  joy  or  a  thrilling  spectacle.  There  seems  to 
be  much  that  is  common  to  all  the  major  emotions,  though 
they  seem  well  differentiated  in  retrospect.  Cannon 
thinks  it  probable  that  the  adrenal  body  is  similarly  in- 
volved in  all  of  them.  The  feeling  of  weakness  that  comes 
in  their  wake  may  be  due  in  part  to  a  subnormal  produc- 
tion of  adrenalin  on  the  part  of  the  exhausted  cells. 

Long  ago  James  wrote  in  his  always  illuminating  way  of 
the  use  and  abuse  of  the  emotions.  He  made  much  of  the 
idea  that  every  emotion  experienced  should  become  a 
motive  for  conduct.    If  it  cannot  be  so  applied,  its  repeti- 


168      THE    NERVOUS    SYSTEM    AND    ITS    CONSEKVATION 

tion  should,  so  far  as  possible,  be  avoided.  This  teaching 
now  appears  to  have  much  more  biologic  truth  in  its  favor 
than  it  seemed  to  have  when  first  pul^lished.  If  the  occa- 
sions in  the  lives  of  animals  when  emotion  is  stirred  are  occa- 
sions for  decisive  action,  we  must  heed  the  moral  and  not 
too  radically  break  with  our  inheritance.  If  the  primitive 
expression  is  out  of  the  question,  we  may  still  be  ingenious 
enough  to  find  a  harmless  or  even  a  profit al)le  substitute. 

Specialists  are  now  laying  all  possible  stress  on  the 
connection  between  nervous  disorders  and  the  suppressed 
or  unsatisfied  tendencies  which  are  believed  to  work  harm 
during  long  periods  of  latency.  The  curbing  of  a  wish, 
when  this  means  not  only  the  check  but  the  annihilation 
of  the  desire,  is  a  noble  exercise  of  inhibition.  The  denial 
of  expression  simultaneously  with  the  continued  enter- 
tainment of  the  wish  is  exceedingly  hurtful.  The  frequent 
experience  of  emotions  which  do  not  secure  any  motor 
outlet  is  also  abnormal.  Anger  maj^  not  lead  to  fighting, 
nor  even  to  scolding,  but  it  may  be  turned  into  a  motive 
for  vigorous  action.  Some  one  has  shrewdly  suggested 
that  the  boy  who  is  heartily  vexed  at  being  set  to  chopping 
wood  or  weeding  the  garden  will  work  all  the  more  swiftly 
and  energetically  for  his  irritation.  If  this  is  the  actual 
result,  and  not  an  ill-natured  dallying  over  the  task,  he 
will  be  much  better  off  at  the  close  than  if  he  had  sulked 
and  idled  until  excused.  "Emotion"  and  "motion"  are 
words  nearly  related,  and  the  conditions  for  which  they 
stand  should  be  related  as  closely. 

The  emotion  of  sympathy  is  one  which  we  readily 
recognize  as  peculiarly  exhausting  to  bear  when  it  cannot 
be  translated  into  acts.  "Let  us  love  not  in  word,  neither 
in  tongue,  but  in  deed  and  in  truth" — there  is  hygiene  as 
well  as  humanity  behind  the  injunction.  Sympathy  with 
suffering  may  in  many  cases  subject  the  one  who  feels  it  to 
a  torture  more  keen  than  that  which  has  occasioned  it. 
Such  vicarious  pain  is  not  to  be  avoided  altogether,  but  it 
is  greatly  alleviated  when  one  finds  something  to  do  for 
the  sufferer.     How  the  useless  torment  of  viewing  dis- 


EMOTION  169 

tress  is  replaced  in  the  physician  by  the  endeavor  to  relieve 
is  set  forth  in  the  exquisite  story  of  "Rab  and  his  Friends" 
— ''pity,  as  an  emotion,  ending  in  itself  or,  at  best,  in  tears 
and  a  long-drawn  breath,  lessens,  while  pity  as  a  motive 
is  quickened,  and  gains  power  and  purpose." 

It  was  with  similar  ideas  that  James  taught  that  the 
pleasure  of  the  drama  or  the  symphony  concert  ought  to 
find  its  application  in  the  better  performance  of  one's  work 
or  the  readier  expression  of  kindness  toward  one's  asso- 
ciates. The  same  may  be  said  of  the  exaltation  felt  in  the 
presence  of  beautiful  natural  scenes.  This  seems  like 
ethical  preaching,  but  it  is  none  the  less  sound  hygiene. 
In  fact,  the  present  age  far  more  than  any  that  has  gone 
before  understands  the  closeness  of  the  parallel.  The 
teaching  with  regard  to  emotion  is,  after  all,  just  that  of 
pedagogics,  that  it  is  not  profitable  to  receive  without 
giving  back.  Reaction  is  the  law  of  the  nervous  system 
from  first  to  last. 

We  have  attempted  to  make  the  point  that  all  emotion 
is  exercise,  and  that,  accordingly,  emotion  in  moderate  and 
reasonable  variety  is  a  source  of  general  development;  in 
short,  of  training.  It  will  be  well  to  show  how  women,  far 
more  frequently  than  men,  are  hkely  to  suffer  from  the 
want  of  such  stimulation.  They  often  work  by  them- 
selves and  lack  the  spur  of  companionship  during  a  large 
part  of  the  day.  Their  friendships  are  seldom  as  warm 
and  comforting  as  those  between  men.  Many  do  not  find 
time  for  the  daily  paper,  and,  with  all  its  faults,  the  press 
causes  its  readers  to  visualize  and  in  imagination  to  enter 
into  the  course  of  stirring  events.  The  husband,  who 
profits  by  the  diversion  of  his  newspaper,  the  little  journey 
to  and  from  his  place  of  business,  a  more  or  less  social 
occupation,  and  a  lively  luncii  party  at  noon,  should  not 
forget  how  colorless  by  contrast  has  been  the  day  of  the 
wife  at  home.  More  deliberate  effort  is  necessary  in  her 
case  than  in  his  to  bring  in  the  needed  elements  of  enthu- 
siasm and  interest.  It  is  peculiarly  unfortunate  that  so 
many  women  are  denied  the  full  benefit  of  the  Sabbath 


170      THE    XEKVOUS    SYSTEM    A.\D    ITS   CONSERVATION 

through  being  requiretl  on  that  day  to  evolve  the  most 
elaborate  dinner  of  the  week.  The  natural  consequence 
of  such  restriction  in  scope  for  the  emotional  life  is  at 
first  loss  of  ambition  and  later  of  endurance  also. 

A  pica  may  be  entered  here  for  singing.  We  Americans 
are  too  self-conscious  to  enter  readilj^  into  this  wholesome 
pleasure.  It  would  do  us  good  to  imitate  the  Germans  and 
make  singing  a  common  feature  of  our  gatherings.  Even 
singing  by  one's  self  may  be  beneficial.  The  advantages 
derived  are  parti}''  those  of  a  general  neuromuscular 
exercise  and  in  part  connected  with  the  very  marked  and 
agreeable  emotional  reaction.  People  who  sing,  though 
it  may  be  quite  badly,  are  apt  to  have  attractive  personal- 
ities. A  charming  old  minister  who  set  the  highest  value 
upon  congregational  singing  once  said  that  the  Scripture 
was  drafted  to  include  the  least  gifted  individuals  in  the 
injunction  to  "make  a  joyful  noise  unto  the  Lord." 

Cannon  has  assembled  many  of  the  facts  concerning 
emotion  in  a  novel  and  suggestive  form.^  After  enumerat- 
ing the  autonomic  manifestations,  so  largely  his  own  dis- 
coveries, he  points  out  that  the  regional  distribution  of 
these  in  the  topography  of  the  nervous  system  is  distinct 
and  curious.  The  outflow  of  impulses  accompanying  the 
major  emotions  is  concentrated  in  the  thoracico-luml^ar  or 
so-called  sympathetic  division.  This  department  contains 
the  fibers  which  command  the  dilation  of  the  pupil,  the 
secretion  of  sweat,  the  addition  of  adrenalin  to  the  blood, 
the  development  of  goose-flesh,  acceleration  of  the  heart, 
reduction  of  blood-flow  in  the  digestive  tract,  and  the  in- 
hibition of  its  activity.  We  have  noted  that  these  changes 
prepare  an  animal  for  exertion.  Even  those  which  seem 
to  have  a  negative  character — as  the  anemia  produced  in 
the  alimentary  canal — may  be  indirectly  helpful,  since 
they  reinforce  the  circulation  in  the  skeletal  muscles. 

Now,  there  are  autonomic  paths  which  start  from  the 
cranial  region  and  which  are,  therefore,  anterior  to  the 
sympathetic.  The  responses  to  stimulation  of  these 
'  American  Journal  of  Psychology,  1914,  xxv,  2.56. 


EMOTION 


71 


paths  are  not  familiarly  recognized  in  tlie  display  of  emo- 
tion. They  include  slowing  of  the  heart,  contraction  of 
the  pupils,  salivation,  and  increased  activity  of  the  alimen- 
tary canal.  They  seem  characteristic  of  periods  of  tran- 
quiUity  rather  than  of  excitement.  Again,  posterior  to  the 
sympathetic,  we  have  the  sacral  autonomic.  In  the 
fibers  comprised  in  this  division  are  those  which  promote 
micturition,  defecation,  and  sexual  reactions.  While  the 
bladder  and  the  rectum  may  fall  under  the  disturbmg 
influence  of  emotions,  their  normal  actions  are  executed 
in  the  absence  of  agitating  conditions. 

Cannon's  grand  generalization  is,  accorcUngly,  to  the 
effect  that  the  thoracico-lumbar  autonomic  has  an  "emer- 
gency function,"  and  that  it  is  employed  in  crises  of  rage, 
fear,  and  pain  to  give  the  animal  the  utmost  command  of 
its  resources.  The  activities  of  the  other  autonomic 
mechanisms  have  to  be  held  in  abeyance  at  such  times, 
and  are  carried  on  only. when  there  is  no  external  cause  of 
distraction.  It  is  urged  that  the  autonomic  accompani- 
ments of  all  the  major  emotions  are  too  nearly  identical 
to  differentiate  them,  and  that  this  fact  restricts  and 
weakens  the  James-Lange  theory.  No  condensed  state- 
ment can  do  justice  to  the  article  referred  to,  which  should 
be  consulted. 

A  manifestation  of  emotion  which  is  of  minor  impor- 
tance, but  which  has  attracted  popular  attention  because 
of  its  picturesque  aspects,  is  found  in  certain  disturbances 
of  ihe  electric  equihbrium  of  the  body.^  It  is  probably 
fair  to  claim  that  all  physiologic  processes  are  attended  by 
quick  shiftings  of  potential.  These  changes  have  been 
extensively  studied  in  nerves,  in  muscles  (including  the 
heart),  and  in  glands.  They  are  of  small  magnitude  and 
must  be  registered  by  delicate  instruments.  If  the  two 
hands  are  plunged  into  cups  of  salt  solution  which  are 
connected  through  a  sufficiently  sensitive  galvanometer, 
there  will  be  evidence  of  electric  instability.    The  rhythm 

1  Wells  and  Forbes,  Archives  of  Psychology,  New  York,  March, 
1911. 


172      THE    NERVOUS   SYSTEM    AND    ITS   C'ONSEIIVATION 

of  the  heart-heat  will  he  reproduced  hy  osciUatioiis  of  the 
indicator,  ^\)h^ltary  muscle  contractions  will  displace  it. 
Now,  if  a  series  of  words  is  spoken  in  the  presence  of  the 
man  whose  hands  are  in  circuit  with  the  galvanometer,  it 
is  likely  that  at  least  a  small  excursion  will  follow  each 
word.  But  some  words  will  have  much  more  power  than 
others  to  give  direction  to  his  thoughts  and  to  arouse  his 
feelings.  The  swing  of  the  galvanometer  will  faithfully 
demonstrate  the  degree  of  the  emotional  response.  Thus, 
if  names  of  girls  are  repeated,  the  suljject  of  the  inquisi- 
torial experiment  may  react  to  each  stimulus  b}^  an  appre- 
ciable sign,  but  he  will  pay  tribute  to  the  name  of  his 
fiancee  by  a  striking  movement  of  the  recorder.  These 
electric  disturbances  are  not  surely  localized,  but  they 
testify  to  the  involvement  of  contractile  or  secreting 
structures — perhaps  of  both — in  the  phenomena  of  emo- 
tion. 


CHAPTER  XIV 
SLEEP 

About  one-third  of  an  average  human  Hfe  is  passed  in 
the  familiar  and  yet  mysterious  state  which  we  call  sleep. 
From  one  point  of  view  this  seems  a  large  inroad  upon  the 
period  in  which  our  consciousness  has  its  exercise:  a  sub- 
traction of  twenty-five  years  from  the  life  of  one  who 
fives  to  be  seventy-five.  Yet  we  know  that  the  efficiency 
and  comfort  of  the  individual  demand  the  surrender  of  all 
this  precious  time.  It  has  often  been  said  that  sleep  is  a 
more  imperative  necessity  than  food,  and  the  claim  seems 
to  be  well  founded. 

The  writer  once  asked  a  psychologist  how  he  would 
define  sleep,  and  received  the  answer,  "Why,  it  is  nothing 
at   ah."     It   has   been   simply   described   as   inattention. 
Both  these  characterizations  turn  upon  the  idea  that  sleep 
is  a  suspension  of  consciousness  and  ignore  its  physiologic 
features.    Our  own  judgment  as  to  whether  we  have  been 
asleep  or  not  is  evidently  based  upon  the  same  concep- 
tion.    If  this  is  the  whole  story,  no  animal  can  be  said  to 
sleep  unless  we  grant  that  it  is  conscious  at  other  times. 
We  readily  recognize  that  sleep  is  more  clearly  a  part  of  the 
lives  of  the  higher  animals  than  of  those  below  them  in  the 
scale,  but  it  is  hard  to  set  fimits  to  its  occurrence.     All 
mammals  and  birds  are  assumed  to  sleep;  probably  the 
reptiles  do,  but  we  do  not  feel  so  sure  about  the  frog  or  the 
fish. 

It  might  be  more  rational  to  reverse  the  order  of  inquiry 
and,  instead  of  asking  how  far  down  in  the  scale  there  is 
sleep,  we  might  ask,  at  what  level  as  we  ascend  the  scale, 
do  we  find  animals  awake?  Is  not  all  life,  below  a  certain 
stratum,  somnambulistic?     An  idea  much  hke  this  has 

173 


174      TIIK    XKUVOUS    SYSTEM    AND    ITS    C'OXSKKVATIOX 

been  expressed  by  Thomson.  It  is,  briefly,  as  follows: 
Sleep  becomes  necessary  at  the  same  stage  in  develop- 
ment where  there  is  the  earliest  entertainment  of  consciovis 
purposes.  Animals  which  are  never  actuated  by  such  pur- 
poses will  not  overdo.  Their  metabolism,  their  Avaste, 
and  repair  will  go  on  in  a  fairly  even  manner,  each  output 
of  energy  being  followed  by  a  prompt  subsidence  of 
activity  to  permit  recuperation.  But  as  soon  as  there  is 
any  germ  of  will,  any  interest  in  the  pursuit  of  an  object, 
the  organism  will  be  spurred  on  until  the  compensatory 
change  has  to  be  of  a  profound  and  long-continued  kind, 
and,  moreover,  has  to  abolish  the  entertainment  of  the 
conscious  purpose  while  it  is  in  progress. 

While  we  cannot  help  emphasizing  the  relation  of  sleep 
to  consciousness,  and,  therefore,  on  the  physiologic  side, 
to  the  cerebrum,  we  are  obliged  to  concede  that  other 
parts  of  the  nervous  system  are  involved.  This  is  plain 
from  the  fact  that  decerebrate  birds  and  mammals  still 
exhibit  an  alternation  of  two  conditions  which  have  the 
outward  aspect  of  sleeping  and  waking.  The  periodic 
depression  is  not  confined  to  the  cortex,  though  a  slight 
change  in  the  chemical  condition  of  the  cerebral  gray 
matter  would  seem  to  be  sufficient  to  produce  the  purely 
psychic  experience  of  going  to  sleep. 

Whatever  may  be  the  essential  condition  of  .sleep,  it  is 
favored  by  the  cessation  of  external  stimulation  and  post- 
poned by  the  action  of  such  disturbances.  It  is  probably 
for  this  reason  that  most  animals  are  disposed  to  sleep 
at  night.  This  will  most  surely  be  the  case  with  those 
which  receive  a  large  share  of  their  guiding  impressions 
through  the  eye.  Normal  man  falls  in  this  class.  His  eyes 
are  his  most  important  receptors,  but  because  of  his  com- 
mand of  artificial  lighting  he  is  not  compelled  to  submit 
tamely  to  the  suggestion  that  he  go  to  sleep  at  sundown. 
He  has  developed  a  curious  habit  of  being  active  far  into 
the  night  and  sleeping  far  into  the  da}',  at  least  in  the 
spring  and  summer  of  the  temperate  zone.  This  tend- 
ency may  suggest  a  whimsical   citation  of  the  first  law 


SLWEP  175 

of  mechanics:  "A  body  in  motion  continues  in  motion, 
a  body  at  rest  continues  at  rest,  unless  acted  on  by  an 
external  force." 

The  purpo.ses  served  by  sleep  are  plain.  It  is  a  state 
in  which  the  local  and  general  losses  of  the  tissues,  which 
have  not  been  fully  met  as  they  have  taken  place,  can  be 
offset.  Bodily  rest  without  sleep  gives  an  opportunity 
for  such  repair  in  the  skeletal  muscles,  but  not  neces- 
sarily in  the  receptor  system,  and  certainly  not  in  the 
cerebrum.  Even  the  skeletal  muscles  are  probably  better 
rested  in  sleep  than  they  can  be  otherwise,  for  their  relax- 
ation is  more  complete.  As  to  the  autonomic  mechan- 
isms, it  is  harder  to  determine  how  far  they  are  granted 
a  remission  of  activity  during  sleep.  We  have  to  bear  in 
mind  the  fact  that  many  of  the  autonomic  influences  are 
inhibitory  in  character,  and  the  interruption  of  such  cur- 
rents would  lead  to  an  actual  increase  of  activity  in  the 
organs  reached  by  the  nerve-fibers.  No  case  of  this  kind 
is  certainly  known,  but  the  principle  helps  us  to  under- 
stand how  there  may  be  no  interference  with  digestion 
while  an  animal  is  sleeping,  as  it  is  likely  to  after  eating 
heavily. 

Many  theories  have  been  advanced  to  account  for  the 
passage  from  the  waking  to  the  sleeping  state.  It  will  be 
helpful  to  consider  what  conditions  other  than  sleep  com- 
monly suspend  consciousness.  Two  suggest  themselves, 
the  one  mechanical  and  the  other  chemical.  One  is  inter- 
ference with  the  circulation  in  the  brain,  and  the  second 
is  anesthesia  by  drugs  carried  through  the  medium  of  the 
blood.  Though  we  may  call  the  first  a  mechanical  cause 
of  unconsciousness,  it  is,  doubtless,  a  chemical  one  at  bot- 
tom, for  lack  of  blood-supply  must  lead  to  chemical  altera- 
tions in  the  neurons.  Fainting  is  an  instance  of  this  action. 
The  other  type  of  influence  may  be  illustrated  by  ether  or 
chloroform  narcosis,  as  well  as  by  the  coma  of  diabetes, 
where  the  acidity  of  the  blood  is  the  source  of  trouble. 
Normal  sleep  has  sometimes  been  thought  of  as  a  swooning 
and  sometimes  as  an  anesthesia.    When  the  former  cause 


17()      THE    NERVOUS    SYSTEM    AND   ITS    CONSERVATION 

is  assumed,  we  have  an  anemia  theon-;  the  alternative  is 
a  theory  of  toxemio. 

The  nightly  experience  of  falling  asleep  does  not  very 
distinetl.y  suggest  fainting.  But  when  the  drowsiness  is 
unusually  compelling  and  unwelcome,  as  when  one  nods 
in  church,  the  resemblance  does  not  appear  so  remote. 
The  rapidity  of  the  passage  from  clear  consciousness  to  the 
realm  of  dreams  or  to  oblivion  favors  the  belief  that  a 
mechanical  factor  has  operated  to  determine  it.  The 
most  natural  assumption  is  that  a  vasomotor  change 
has  taken  place.  Howell  has  pointed  out  that  such  a 
change  may  be  due  to  fatigue  of  the  vasomotor  center. 
During  our  waking  hours  this  part  of  the  autonomic 
system  is  required  to  respond  to  frequent  and  varying 
demands.  Some  of  its  duties  have  been  indicated  in  an 
earlier  chapter. 

If  the  center  is  really  subject  to  fatigue,  we  may  sup- 
pose that  it  eventually  becomes  difficult  to  stimulate  it 
sufficiently  to  maintain  the  normal  arterial  tone.  If  it 
lapses  from  its  average  condition,  the  blood-pressure  will 
decline  and  the  flow  will  proceed  more  slowly  through 
the  widened  vessels.  In  the  brain,  encased  as  it  is  in  a 
rigidly  walled  enclosure,  the  slow  flow  wall  be  in  vessels 
which  cannot  materially  widen.  Hence,  the  brain  suppl}^ 
will  be  reduced  and  the  maintenance  of  its  activities 
threatened.  It  remains  possible  in  an}'  ordinary  case  to 
spur  the  center  to  renewed  action,  to  raise  the  general 
pressure,  and  so  to  drive  the  blood  once  more  with  an 
adequate  velocity  through  the  capillaries  of  the  brain. 

Drowsiness  is  the  sul^jective  sign  of  the  slowing  cir- 
culation in  the  cerebrum.  In  fighting  it  off  one  resorts 
instinctively  to  the  employment  of  external  stimulation. 
This  is  the  object  attained  by  taking  a  slightly  uncom- 
fortable position,  by  raising  one's  eyes  to  the  light,  and 
by  moving  parts  of  the  body.  The  exclusion  of  stimuli, 
conversely,  favors  the  relaxation  of  the  vascular  system. 

'  "Text-book  of  Physiology,"  Fifth  Edition,  W.  B.  Saunders  Co., 
Philadelphia,  1913. 


SLEEP  177 

When  we  court  sleep  we  seek  quiet  and  darkness.  By 
lying  down  we  reduce  to  a  minimum  the  inflowing  im- 
pulses from  muscles,  tendons,  and  joints.  We  avoid  ex- 
tremes of  temperature.  We  interrupt,  so  far  as  we  may, 
the  more  vivid  trains  of  thought.  Thus,  in  favorable  cases, 
we  withdraw  from  the  vasomotor  center  the  nerve-currents 
which  prompt  it  to  react  upon  the  blood-vessels,  and  we 
are  rewarded  by  a  welcome  change  in  the  character  of  our 
consciousness,  if  not  by  its  actual  suspension. 

The  fact  that  one  can  be  awakened  at  any  time  by 
stimuli  supports  the  theory  that  the  immediate  cause  of 
sleep  is  the  slackening  of  the  blood-flow  through  the  brain. 
A  state  of  general  poisoning  could  not  be  done  away  with 
on  the  instant  by  the  stimulation  of  afferent  paths. 
Nevertheless,  the  acceptance  of  the  vasomotor  hypothesis 
leaves  a  place  for  the  toxemia  theories.  It  is  the  accumu- 
lation of  chemical  compounds,  fatigue  substances,  in  the 
body  fluids  and  perhaps  in  the  protoplasm  itself  that  leads 
up  to  the  central  failure.  We  have,  therefore,  to  distin- 
guish between  the  cause  of  the  approach  of  sleep,  which  is 
metabolic,  and  that  of  its  onset,  which  is  mechanical. 
It  seems  to  be  the  distribution  of  the  fatigue  substances 
rather  than  their  actual  amount  which  makes  sleep  a 
pressing  necessity.  We  know  that  we  may  be  very  tired 
and  find  sleep  impossible. 

When  the  ties  between  the  outer  world  and  the  indi- 
vidual consciousness  are  severed  as  one  sinks  to  sleep 
there  is  an  interesting  and  fairly  definite  order  in  the 
process.  Muscular  control  is  lost  before  sensation;  there 
is  an  interval  of  delicious  relaxation  of  which  one  is 
pleasantly  aware.  Shortly  the  cutaneous  sensibility  is 
gone,  while  the  knowledge  of  the  position  of  the  extremi- 
ties lingers  for  a  little.  Under  such  circumstances  one 
still  reahzes  the  posture,  but  not  the  contact  with  the 
bed.  Havelock  Elhs^  has  suggested  that  this  apparent 
absence  of  any  support  may  be  explained  by  the  dreaming 
consciousness  as  the  experience  of  floating  in  space  or  of 
1  "The  World  of  Dreams,"  Houghton,  Mifflin  &  Co.,  Boston,  1911. 
12 


178      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

fallinji;,  two  very  coininou  impressions,  llcai'ing  is  the 
latest  means  of  communication  between  the  world  without 
and  the  isolated  mind.  It  is  likewise  the  first  channel  to 
be  reopened  as  one  is  roused  or  wakes  gradually  from 
sleep. 

The  depth  of  sleep  at  different  times  in  the  course  of  tlu> 
night  has  often  been  tested.  In  the  trials  most  frequently 
referred  to,  the  measurement  was  based  on  the  loudness  of 
the  sound  necessar}^  to  awaken  the  sleeper.  All  observers 
have  agreed  that  the  deepest  sleep,  as  indicated  by  such 
methods,  comes  quite  earl}^  probably  within  the  second 
hour,  if  not  the  first.  We  know  that  if  we  are  awakened 
within  this  period  the  experience  is  one  of  violent  subject- 
ive and  bodily  disturbance.  The  nervous  shock  is  such 
as  to  make  it  hard  to  compose  one's  self  again.  It  is  a  very 
different  matter  to  be  aroused  from  the  later  and  shallower 
sleep;  then  the  response  to  a  call  is  easily  obtained,  but, 
unhappily,  it  is  correspondingly  easy  to  sink  back  to 
sleep. 

After  the  first  deep  sleep  there  is  a  shoaling  which  is 
about  as  rapid  as  the  previous  subsidence  into  the  depths. 
Within  three  hours  of  the  beginning  a  condition  is  reached 
in  which  there  is  marked  sensitiveness  to  stimulation. 
Opinions  differ  as  regards  the  later  behavior  of  the  nervous 
system.  According  to  one  set  of  data  there  is  a  gradual 
and  progressive  reduction  of  the  depth  of  sleep  during  the 
three  or  four  additional  hours  of  its  continuance.  Others 
have  noted  a  second  deepening  toward  morning.  This 
last  description  appears  to  fit  in  with  a  great  deal  of  in- 
dividual experience;  a  wakeful  time  may  be  passed 
through  about  5  o'clock,  and  it  may  be  harder  to  get  up 
two  hours  later  than  it  would  have  been  at  dawn.  A 
German  writer,  accepting  the  double-peaked  curve  as  nor- 
mal, has  referred  it  to  the  impression  made  upon  the 
centers  when  the  infant  woke  once  each  night  to  be  fed. 
Little  children  who  no  longer  wake  at  this  time  are  apt  to 
show  a  restless  interval  between  two  periods  of  heavy 
slumber. 


SLEJiir 


179 


On  any  theory  we  should  expect  to  find,  as  in  fact  we  do, 
that  the  greatest  depth  of  sleep  would  be  soon  reached 
and  passed.  There  should  be  a  steady  gain  in  the  direction 
of  the  sweeping  away  of  fatigue  substances  and  a  steady 
improvement  in  the  capacity  for  reaction,  which  is  what  we 
measure  when  we  induce  waking.     It  does  not  follow  that 


Fig.  24. — A  schematic  diagram  of  Mosso's  pletbysmograph  for 
the  arms:  a,  The  glass  cyhnder  for  the  arm,  with  rubber  sleeve  and 
two  tubulatures  for  filhng  with  warm  water;  s,  the  spiral  spring 
swinging  the  test-tube,  t.  The  spring  is  so  calibrated  that  the  level 
of  the  liquid  in  the  test-tube  above  the  arm  remains  unchanged  as 
the  tube  is  filled  and  emptied.  The  movements  of  the  tube  are  re- 
corded on  a  drum  by  the  writing  point,  p.     (Howell.) 


the  time  passed  in  shallow  sleep  can  be  much  shortened 
without  detriment.  The  experiments  cited  show  only 
that  certain  mechanisms  require  less  than  three  hours  to 
regain  almost  their  full  irritability;  there  are  many  more 
which  may  need  a  longer  exemption  from  the  demands  of 
the  waking  state. 

The  vasomotor  changes  which  mark  the  coming  on  of 


180      THE    .NERVOUS    SYSTEM    AND    ITS    CONSERVATION' 

sleep  and  its  departure  have  been  demonstrated  in  the 
normal  human  being  by  an  indirect,  but  sensitive,  method. 
Tliis  is  the  use  of  the  instrument  known  as  the  plethysmo- 
graph  (Fig.  24),  which,  in  its  usual  form,  is  a  glass  cylinder 
designed  to  accommodate  the  hand  and  forearm  of  the 
subject.  A  tight  but  comfortable  closure  at  the  end 
toward  the  elbow  is  secured  and  the  whole  is  filled  with 
water.  A  delicate  gage  is  connected  with  the  interior 
and  any  displacement  or  drawing  back  of  water  is  made 
evident.  A  displacement  must  mean  an  increase  in  the 
volume  of  the  arm  and  hand,  a  withdrawal  must  indicate 
a  shi'inkage.  Such  changes  in  volume,  when  they  occur 
at  all  rapidl}^,  may  be  ascribed  to  changes  in  the  amount 
of  blood  in  the  part.  More  gradual  changes  might  be  due 
to  variations  in  the  quantity  of  the  lymph. 

When  a  person  schools  himself  to  go  to  sleep  with  his 
arm  enclosed  in  a  plethysmograph  it  is  found  that  a 
marked  dilation  of  the  member  occurs  at  about  the  time 
when  the  threshold  is  crossed.  This  testifies  to  a  diminu- 
tion of  the  tonic  activity  of  the  vasoconstrictor  center. 
It  has  already  been  pointed  out  that  such  a  slackening 
will  result  in  a  more  sluggish  cranial  circulation.  Hence 
it  is  inferred  that  when  the  record  from  the  plethysmo- 
graph shows  a  widening  of  the  vessels  in  the  arm  there  is 
a  simultaneous  flagging  of  the  blood-supply  to  the  brain. 
When  waking  occurs  there  is  a  sharp  contraction  of  the 
arm.  It  is  very  significant  that  external  stimuli  applied 
during  sleep,  but  not  sufficing  to  rouse  the  sleeper,  never- 
theless cause  vasomotor  responses.  In  the  experiments 
directed  by  Howell,  he  himself  being  the  subject,  the 
watcher  at  the  bedside  saw  that  occasional  noises  and 
vibrations  interrupting  the  quiet  of  the  night  registered 
themselves  through  the  distinct  narrowing  of  the  vessels 
of  the  arm  which  they  called  forth.  The  reaction  might 
be  described  as  a  threat  of  v/aking. 

On  the  side  of  hygiene  there  is  much  to  be  said  of  sleep. 
Questions  frequently  asked  and  not  at  all  easy  to  answer 
are:    How  nmch  sleep  is  best  and  how  far  do  individuals 


SLEEP  181 

differ  in  their  requirement?  How  can  one  know  whether 
enough  sleep  is  taken?  Is  it  possible  to  sleep  too  much? 
All  these  are  related  questions  and  all  are  important,  but 
intelhgent  people  will  be  likely  to  answer  them  in  very- 
different  ways.  We  may  attempt  to  deal  with  the  last  one 
first,  and  we  will  venture  the  assertion  that  it  is  possible 
to  sleep  more  than  is  best.  The  fact  that  it  is  found  diffi- 
cult to  get  up  in  the  morning  is  by  no  means  a  sure  sign 
that  more  sleep  should  be  taken.  It  may  be  only  a  sign  of 
laziness.  It  is  better  to  be  guided  by  the  evening  feeling 
and  particularly  by  the  demand  of  the  eyes  for  a  release 
from  their  task. 

The  disciples  of  Horace  Fletcher  claim  that  one  of  the 
benefits  realized  when  a  low  diet  has  been  adopted  is 
found  in  the  fact  that  the  hours  of  sleep  may  be  shortened 
without  making  inroads  upon  health.  The  obvious  sug- 
gestion is  that  a  part  of  the  sleep  of  average  men  is  a  coma, 
an  avoidable  intoxication,  due  to  an  excess  of  narcotizing 
substances  absorbed  from  the  burdened  intestine.  Whether 
this  is  a  typic  condition  or  not,  it  is  probably  exempfified 
by  some  heavy  eaters.  The  picture  of  the  carnivorous 
animal  gorged  with  concentrated  food  and  crawling  away 
for  a  long  sleep  is  familiar  enough.  Many  young  men  and 
women  who  supposed  that  certain  hours  of  sleep  were 
necessary  to  their  efficiency,  have  discovered,  after  mar- 
riage and  the  coming  of  children,  that  they  are  capable  of 
much  more  work  with  much  less  sleep  than  they  formerly 
believed. 

With  advancing  age  the  need  for  sleep  seems  generally 
to  diminish.  In  the  Preacher's  classic  description  the  old 
person  is  said  to  "rise  up  at  the  voice  of  the  bird."  Many 
readers  will  recall  the  uneasy  habits  of  the  aged,  who 
cannot  lie  peaceably  in  bed  until  the  younger  members  of 
the  family  consider  it  time  to  get  up,  but  are  found 
bustling  feebly  about  imaginary  duties  in  the  early  hours 
of  the  morning.  The  nervous  system  in  which  the  decom- 
position processes  have  become  lessened  in  intensity  has 
less  need  of  the  compensatory  state. 


1S2      TIIK    MOIlVOrS    SVSTlvM    AM)    ITS    CON'SKHVATIOX 

Js  llu'iv  any  scicutilit'  basis  for  the  okl  tc'ai-hin>>;,  "Early 
to  bed  and  early  to  rise"?  It  would  seem  at  first  as 
though  sleep  at  one  time  should  have  as  much  virtue  as  at 
another.  Still  the  ancient  maxim  may  have  a  certain 
foundation.  To  be  up  early  and  to  ^o  "early  to  bed" 
means  that  the  use  of  artificial  light  will  be  reduced  to  a 
minimum.  It  is  not  likely  that  any  substitute  for  day- 
light can  be  found  which  will  not  impose  a  severer  tax 
upon  the  e^'es  than  does  their  natural  form  of  stimula- 
tion. Whatever  tires  the  eyes  has  a  widespread  and  de- 
pressing influence  upon  the  whole  nervous  system.  Again, 
lying  abed  late  in  the  morning  has  the  disadvantage  that 
the  sleeper  is  likely  to  be  affected  by  light  and  noises  which 
may  deprive  his  rest  of  some  of  its  potenc}^  for  good,  even 
though  they  do  not  interrupt  it. 

Neuron  Theories  of  Sleep. — We  have  regarded  sleep  as 
a  state  induced  indirectly  l^y  fatigue  substances  acting 
upon  the  system  and  directly  by  the  failure  of  an  adequate 
cerebral  circulation.  Other  aspects  of  the  condition  insiy 
be  selected  for  emphasis.  All  the  facts  of  sleep  might  be 
explained  by  the  conception  of  varying  synaptic  resistance. 
The  establishing  of  gaps  in  the  motor  paths  would  remove 
the  muscles  from  central  control.  Similar  gaps  anywhere 
along  the  paths  which  conduct  impulses  from  the  receptors 
would  cause  sensory  paralysis  for  the  time.  Thought,  in 
the  absence  of  the  means  of  present  guidance  from  the 
external  world  and  deprived  of  the  power  to  express  itself 
through  the  neuromuscular  mechanism,  must  be  limited 
to  a  rehearsal  of  memories  and  should  take  on  the  character 
of  dreaming.  We  should  expect  that  a  further  impairment 
of  intercourse  among  the  various  regions  of  the  cerebruni 
must  suspend  even  this  kind  of  psychic  activity. 

Reasoning  along  the  lines  just  indicated,  certain  physiol- 
ogists have  pictured  the  passage  from  waking  to  sleeping 
as  due  to  the  interposition  of  extra  resistance  at  the 
synapses.  The  idea  was  first  expressed  as  a  literal  snapping 
of  connections  between  the  discharging  and  receptive 
processes   of  the   neurons,   but   this   has   come  to   seem 


SLEEP  18ft 

highly  improbable.  Still,  the  conception  has  a  symbolic 
if  not  a  literal  value.  We  have  seen  in  our  general  discus- 
sion of  fatigue  that  the  synapses  may  be  regarded  as  links 
of  low  endurance,  and  this  makes  it  reasonable  to  give  them 
a  place  in  our  hypotheses  of  sleep. 

It  is  curious  to  find  that  the  idea  that  the  junctions  of 
the  neurons  may,  in  some  sense,  open  and  close  has  been 
used  in  two  lines  of  speculation  of  a  distinctly  contrasted 
character.  According  to  the  more  familiar  view — already 
outlined — it  is  the  breaking  apart  of  the  nervous  units 
which  paralyzes  objective  and  subjective  activity.  An- 
other theory,  originating  in  Italy  and  not  widely  known 
here,  makes  precisely  the  contrary  assumption,  that  sleep 
is  the  accompaniment  of  an  extensive  commingling  of 
cell  processes.  The  establishment  of  new  connections 
between  the  neurons  might  explain  the  confusion  and 
irrational  combinations  occurring  in  dreams.  The  general 
failure  of  reactions  and,  finally,  of  consciousness  itself 
might  be  explained  as  due  to  a  dissipation  of  the  nerve- 
currents  in  so  many  paths  that  there  should  nowhere  be 
any  effective  intensity.  Waking,  then,  might  be  pictured 
as  the  resvmption  of  intercourse  among  the  neurons,  or  as 
the  restriction  of  intercourse  to  the  usual  serviceable  chan- 
nels after  a  period  of  disorderly  diffusion. 

A  mill  is  usually  stopped  by  closing  the  gates  and  inter- 
rupting the  stream  that  has  been  turning  its  wheels,  but 
it  could  be  stopped  by  opening  sluices  in  the  dam  and 
diverting  a  large  share  of  the  water.  The  two  possi- 
bilities correspond  roughly  with  the  neuron  theories  of 
sleep.  Either  a  cessation  or  a  scattering  of  impulses  within 
the  brain  may  conceivably  result  in  unconsciousness. 
The  second  theory  is  better  adapted  to  an  explanation  of 
dreams,  a  matter  to  which  we  must  now  turn. 


CHAPTER   XV 

DREAMS 

Most  people,  even  though  they  may  be  much  interested 
in  the  achievements  of  science,  will  probably  be  found 
quite  skeptical  concerning  the  idea  that  dreams  are 
worthy  of  any  serious  notice.  In  common  judgment  it  is 
a  weakness  to  think  or  talk  much  about  the  strange  scenes 
we  witness  in  sleep.  This  feeling  is  probably  the  result  of 
emancipation  from  the  superstitious  faith  in  the  revealing 
virtue  of  dreams  which  was  once  universal.  Tawdry 
books,  purporting  to  give  a  basis  for  the  interpretation  of 
dreams  and  attaching  an  occult  significance  to  every 
common  object  seen  by  the  dreamer,  are  still  circulated. 
However  fanciful  these  publications  may  be,  their  purpose 
is  not  wholh^  unlike  that  of  a  rapidly  increasing  mass  of 
sober  scientific  writing. 

We  cannot  follow  this  subject  far,  but  it  would  be  unwise 
to  omit  all  reference  to  dreaming,  for  it  is  fruitful  of  sug- 
gestions concerning  hygiene.  One  of  the  most  obvious 
has  to  do  with  the  general  content  of  the  dream.  Havelock 
Ellis^  classifies  dreams  as  follows:  (1)  There  are  those 
which  are  determined  by  the  bodily  conditions  existing 
at  the  moment;  these  may  be  called  somatic,  presentative 
dreams.  (2)  There  are  those  which  are  shaped  by  stimuU 
acting  from  without;  they  may  be  called  external,  presen- 
tative dreams.  Other  dreams  are  not  clearly  related  to 
present  circumstances,  but  are  mosaics  of  memories. 
Ellis  calls  such  dreams  ?'epresentative  and  su})divides 
them  into  two  classes,  the  recent  and  the  remote.  It  is 
a  matter  of  moment  whether  one's  memory  dreams  are  of 
the  recent  or  the  remote  kind. 

'  "The  World  of  Dreams,"  Houghton,  Mifflin  &  Co.,  Boston,  1911. 
184 


DREAMS  185 

A  man  who  is  happy  and  not  overtired,  who  is  meeting 
his  obhgations  with  reasonable  ease  and  success,  is  likely, 
when  he  goes  to  sleep,  to  encounter  persons  and  scenes 
quite  other  than  those  he  has  lately  known.  Unexpected- 
ness is  the  foremost  quaUty  of  his  dreaming  experiences. 
If  he  is  skilled  in  unravelling  the  composition  when  he 
reviews  it  after  waking,  he  may  be  able  to  detect  many 
of  the  sources  and  to  convince  himself  that  they  belong  to 
relatively  distant  periods  in  his  career.  It  will  usually  be 
his  impression  that  he  has  not  been  thinking  at  all  of  the 
matters  which  have  been  brought  before  him  in  his 
dreams. 

If  he  is  seriously  tired,  anxious,  and  overwrought,  he 
may  be  compelled  to  attend  to  visions  of  an  entirely 
different  class.  Such  a  man  may  continue,  in  dreams,  to 
pursue  the  interests  of  his  daily  life.  The  same  problems 
which  he  had  to  face  when  waking  confront  him  in  his 
sleep.  The  chess-player  who  has  finished  a  hard  game 
shortly  before  going  to  bed  may  find  the  board  again  set 
before  him  and  be  forced  to  consider  the  possible  results 
of  each  move  through  a  long  series.  When  he  rouses 
himself  he  feels  that  he  has  not  rested  well.  In  the  same 
way  one  in  grief  or  fear  may  still  entertain  these  feelings 
and  ponder  their  causes  while  he  sleeps.  Now,  all  dreaming 
is  partial  insomnia,  but  there  can  be  no  question  that  it  is 
better  to  be  awake  to  novel  and  diverting  thoughts  than  to 
find  no  release  from  the  pressing  concerns  of  one's  routine 
existence.  "Recent  representative"  dreams  clearly  consti- 
tute an  unprofitable  overtime  performance  on  the  part 
of  some  of  the  brain  mechanisms. 

The  statement  just  made  suggests  that  it  may  not  be 
wholly  whimsical  to  claim  that  dreams  of  the  other  (re- 
mote) order  afford  some  of  the  elements  of  a  vacation. 
The  body  does  not  find  the  same  wholesome  change  of 
environment  and  exercise  as  though  an  actual  outing 
were  taken,  but  the  purely  mental  content  may  be  much 
the  same.  Dreams  may  be  at  least  as  beneficial  as  a  mov- 
ing-picture show,  which,  in  fact,  they  greatly  resemble. 


ISO      THE    XEKVOLS    SYSTEM    AND    ITS    CONSERVATION 

So  long  as  they  have  the  unexpected  character,  their  oc- 
currence does  not  seem  to  indicate  that  there  is  any  failure 
to  recuperate  the  powers  of  those  nerve-complexes  on  which 
the  strain  of  the  ensuing  day  must  fall.  It  may  be 
asserted  that  dreamless  sleep  is  the  ideal,  but  we  do  not 
know  surely  that  it  is  ever  realized.  People  who  say  they 
never  dream,  more  probably  dream  and  forget.  We  know 
how  uncertain  at  best  is  our  recollection  of  most  dreams. 
The  impressions  seem  to  be  destroyed  by  the  strong  light 
of  day  asi  though  they  were  images  upon  a  photographic 
plate.  Much  as  we  have  to  develop  our  negatives  in 
rooms  dimly  lighted  by  selected  rays,  we  have  to  rehearse 
our  dreams  in  the  half-waking  condition  at  dawn  if  we  are 
to  make  them  our  permanent  possession.  This  does  not 
imply  want  of  vividness  in  dreams  when  they  are  first 
experienced;  Ellis  is  apparently  justified  in  his  striking 
aphorism:  "Dreams  are  real  while  they  last;  can  we  say 
more  of  life?" 

The  writer  once  had  occasion  to  discover  how  completely 
a  lapse  of  memory  may  create  the  impression  that  there 
has  been  unconsciousness.  Nitrous  oxid  had  been  given 
for  the  extraction  of  two  teeth.  When  he  came  to  him- 
self he  told  the  dentist  that  he  was  much  gratified  by  the 
entire  success  of  the  anesthesia.  He  left  the  office  with 
the  same  feeUng  of  satisfaction.  On  the  street  a  few  min- 
utes later  he  recalled  with  appalling  distinctness  the  pain 
of  the  second  extraction.  No  impression  of  the  first 
operation  ever  returned.  It  is  disquieting  to  think  that 
one  may  suffer  severely  and  then  report  in  good  faith  that 
one  did  not,  but  it  is  the  same  with  dreaming. 

The  subject  matter  of  dreams  may  be  of  considerable 
assistance  in  answering  a  very  important  question.  A 
person  who  wakes  day  after  day  with  feelings  of  weariness 
and  incapacity  may  be  either  indolent  or  tired.  It  is 
likely  that  the  sensations  are  much  the  same  in  the  two 
cases,  and  yet  it  is  necessary  that  the  two  conditions  shall 
be  distinguished.  Clearly  enough,  mischief  will  be  done 
if  one  who  is  reall}^  fatigued  and  in  need  of  more  rest 


DREAMS  187 

mercilessly  condemns  himself  for  laziness  and  redoubles 
his  efforts  to  overcome  the  inertia.  On  the  other  hand,  a 
man  who  is  actually  lazy  and  failing  to  make  the  most  of 
himself  may  be  led  into  habits  of  self-pity  and  self- 
indulgence  by  concluding  that  he  is  seriously  tired. 
When  face  to  face  with  this  problem  it  is  well  to  ask 
whether  the  dreams  have  been  mostly  of  the  recent  or  the 
remote  type.  If  they  have  been  filled  with  the  cares  of 
the  day,  there  is  good  ground  for  assuming  that  cumula- 
tive nervous  fatigue  is  developing.  If  they  are  recalled 
as  fantastic,  varied,  and  curious,  the  conclusion  may  be 
less  welcome,  but  also  less  ominous. 

As  to  dreams  of  the  "presentative  type" — those  in  which 
immediate  circumstances  connected  with  the  body  itself 
and  sources  of  stimulation  close  at  hand  are  concerned — 
the  most  interesting  facts  established  are  those  with 
regard  to  symbolic  depiction  of  the  causative  conditions. 
It  is  quite  plain  that  the  dreaming  mind  usually  refers 
all  its  experiences  to  external  affairs.  It  gives  them  an 
objective  existence.  Suppose,  for  example,  that  a  man  has 
an  uncomfortably  palpitating  heart.  When  he  is  awake 
he  is  in  no  doubt  of  the  actual  nature  of  the  case,  but 
when  he  falls  asleep  and  dreams,  it  is  not  to  feel  that  his 
heart  is  rapid  and  irregular,  but  to  view  some  scene  sug- 
gestive of  difficult  action,  it  may  be  a  horse  struggling  to 
draw  a  load  up  a  hill  or  a  laborer  grappling  with  a  heavy 
stone.  The  writer  once  lay  thinking  of  the  physiologic 
action  of  the  heart  as  sleep  drew  near,  and  when  the 
border-line  was  crossed  he  saw  at  once  a  huge  pulley- 
block.  It  was  so  good  a  symbol  of  a  weight-raising  device 
that  he  awoke  with  lively  gratification. 

According  to  the  same  principle,  the  victim  of  indi- 
gestion does  not  think  while  he  dreams  that  he  is  suffering, 
but  he  becomes  a  witness  of  some  spectacle  of  violence  or 
horror.  Dreams  referable  to  distention  of  the  bladder 
symbolize  the  real  trouble  in  naive  and  amusing  ways. 
One  who  was  in  such  a  case  thought  that  he  turned  on  a 
faucet  which  did  not  run.     The  trivial  dream  perfectly 


188      THE    XERVOrS   SYSTEM    AND    ITS    CONSERVATION 

figurcil  the  neetl  that  existed  and  the  desirable  inhibition 
that  postponed  its  satisfaction,  but  the  facts  were  made 
to  appear  as  external  to  the  dreamer's  person.  Thus  we 
are  constantly  detaching  portions  of  the  self  and  treating 
them  as  separate  objects  of  attention.  Ellis  has  discern- 
ingh'  pointed  out  that  this  tendency  is  not  entirely  absent 
from  the  waking  mind  and  that  it  may  become  a  con- 
spicuous one  at  times.  This  is  particularly  true  when  the 
temperament  verges  toward  the  neurasthenic. 

The  unfortunate  person  who  is  mentally  depressed  is 
prone  to  charge  upon  others  the  faults  which  are  his  own. 
When  he  is  quick  tempered,  he  is  convinced  that  they  are 
impatient.  Precisely  as  the  dreamer  does,  he  fails  to  recog- 
nize that  the  matter  which  offends  and  outrages  him  is 
part  of  himself.  If  he  feels  better  for  a  while,  he  concludes 
that  his  housemates  have  become  more  thoughtful  and 
kind.  It  is  harder  for  him  to  recognize  his  own  respon- 
sibility than  it  is  for  any  of  us  to  realize  that  the  rising  and 
setting  of  the  sun  are  illusions  due  to  the  movement  of 
our  planet.  It  may  be  added  that  it  is  even  more  im- 
portant to  conquer  the  tendency  to  self-deception  in  the 
first  instance  than  in  the  second.  The  man  who  can 
make  the  correct  allowance  for  his  own  ups  and  downs 
while  he  sits  in  judgment  on  others  best  deserves  to  be 
considered  awake. 

We  are  told  by  certain  writers  of  the  present  time  that 
dreams  are  reliable  sources  of  information  for  the  special- 
ist regarding  many  facts  of  personal  history  and  exist- 
ing tendencies  which  the  patient  would  prefer  to  hide. 
Dreams  form  a  large  share  of  the  material  used  for  diag- 
nosis by  the  psychanalysts.'  It  would  be  presumptuous 
for  a  lay  writer  to  criticize  their  principles,  which  have 
often  been  justified  by  the  success  of  their  work.  Never- 
theless, it  may  be  said  that  one  who  reads  their  exposi- 
tions without  special  training  is  likely  to  conclude  that 
psychanalysis  is  the  art  of  putting  the  worst  possible 
construction  upon  all  that  the  subject  thinks  or  dreams. 

'  Brill,  "Psychanaly.si.s,"  ^^'.  B.  SnuiKlers  Co.,  Philadelphia,  1912. 


DREAMS  189 

According  to  Freud  and  his  school,  sexual  impulses 
are  determinative  in  the  shaping  of  most  dreams.  In  the 
troubled  consciousness  of  the  dreamer  there  are  present 
at  once  the  current  of  desire  and  the  sense  of  the  restraint 
which  is  habitually  imposed  upon  it.  Both  are  disguised 
almost  beyond  recognition,  for  the  dreaming  mind  is  cu- 
riously disingenuous  and  indirect.  The  concealment  is  so 
effectual  that  the  average  reader  does  not  readily  accept 
the  interpretations  placed  upon  the  dream  imagery  by  the 
modern  successors  of  Joseph  and  Daniel.  It  seems  as 
though  people  of  an  introspective  turn  might  do  them- 
selves serious  injustice  by  applying  too  rigorously  the 
Freudian  ideas  to  self-examination. 

For  such  there  are  certain  consoling  considerations. 
First  of  all,  it  may  be  stated  that  the  relation  between  the 
waking  and  the  dreaming  life  of  a  man  who  is  approxi- 
mately normal  is  one  of  contrast  rather  than  one  of  resem- 
blance. Therefore,  if  a  man  seems  to  display  a  tendency 
to  cowardice,  frivolity,  deceit,  or  sensuality  in  his  dreams, 
it  may  be  because  these  evil  traits  have  been  decisively 
subordinated  in  his  waking  hours  to  their  very  opposites. 
It  is  only  when  the  will  is  in  abeyance  that  they  can  be 
brought  to  the  fore.  It  is  the  best  of  us  that  goes  to  sleep 
most  soundly,  and  if  there  is  a  shocking  deficiency  in 
generosity  and  renunciation  in  the  apparent  character 
of  the  dreamer,  it  may  be  that  the  instruments  of  these 
faculties  are  plunged  into  a  narcosis  which  is  the  sign  of 
their  continuous  exercise  during  the  day.  It  is  reasonable 
to  suppose  that  in  health  the  parts  of  the  complex  mech- 
anism which  are  most  employed  while  one  is  awake  will  be 
most  profoundly  restrained  from  action  when  sleep  has 
come. 

For  similar  reasons  it  is  unjust  to  conclude  from  the 
unworthy  impulses  of  a  man  in  delirium  that  his  previous 
life  has  been  one  of  hypocrisy  and  duplicity.  It  may 
well  be  that  he  has  been  master  of  the  situation  until  his 
fine  powers  have  been  temporarily  dissipated.  We  must 
bear  in  mind  that  virtue  does  not  consist  in  the  inability 


190      THE    NEKVOllS   SYSTEM    AND    ITS    CONSERVATION 

tg  I'onceivo  of  misconduct,  but  rather  in  the  strength  to 
refrain  from  it  and  to  "overcome  evil  with  good."  This 
is  eminently  true  of  the  sexual  life,  and,  even  if  the  claims 
of  Freud  are  fully  accepted,  it  does  not  follow  that  men 
need  lose  self-r(>spect  or  become  cynical  rejiarding  the 
high  principles  b}'  which  the  lives  of  their  associates  are 
governed. 

We  have  quoted  the  statement  that  sleep  is  inattention. 
By  contrast,  the  state  of  complete  waking  may  be  regarded 
as  one  of  attention,  and,  more  precisely,  of  attention  of  the 
active  order.  Psychologists  distinguish  active  from  passive 
attention,  the  former  requiring  the  voluntary  selection  of 
its  objects  and  the  removal  of  their  competitors  by  a 
process  of  inhibition.  Passive  attention  is  that  which  is 
involuntarily  yielded  to  stimuli  which  we  are  unable  to 
ignore.  This  is  clearly  the  case  when  we  dream;  we  are 
not  able  to  follow  up  the  features  of  the  dream  which  in- 
terest us,  but  are  compelled  to  shift  our  thought  to  others 
which,  in  turn,  elude  our  scrutiny.  Ellis  has  said  that 
dreams  have  always  the  character  of  dissolving  views. 
Objects  which  excite  our  curiosity  persist  in  fading  away 
and  becoming  overlaid  by  new  ones  seemingly  unrelated 
to  the  first. 

We  have  spoken  chiefly  of  the  part  played  in  dreams  by 
memories  and  bodily  conditions.  The  special  sense  organs 
doubtless  bear  their  part.  This  is  true  even  of  the  eyes, 
which  are  sources  of  vague  sensation  even  when  closed. 
It  is  believed  by  many,  including  Bergson,  that  the  glim- 
mering effect  which  anyone  may  notice  on  shutting  the 
eyes  is  quite  influential  in  suggesting  the  scenery  of 
dreams.  It  may  be  thought  a  very  limited  source  for 
such  elal)orate  phenomena,  but,  as  Bergson  points  out,  it 
is  our  habit  when  awake  to  fill  in  the  details  of  what  we 
see  in  scant  outline.  Dreams  influenced  by  sounds  are 
rather  common,  and  serve  to  raise  interesting  questions 
as  to  whether  we  recall  our  dreams  as  they  actually  oc- 
curred or  arrange  their  conteiits  in  a  new  order.  To  use 
an  illustration  from  Ellis:  A  man  dreams  that  heenhsts  in 


DREAMS  191 

the  army,  goes  to  the  front,  and  is  shot.  He  is  awakened 
by  the  slamming  of  a  door.  It  seems  probal)le  that  the 
enhstment  and  the  march  to  the  field  are  theories  to  ac- 
count for  the  report  which  really  caused  the  whole  train 
of  thought,  though  it  seemed  to  be  its  latest  item. 

A  dentist  made  the  following  experiment  twice  with  the 
same  results:  While  a  patient  was  inhaling  nitrous  oxid 
the  names  of  the  stations  on  a  local  railroad  line  were 
repeated  to  him.  When  consciousness  returned  he  was 
asked  what  he  had  dreamed.  In  each  case  the  reply 
was,  "I  thought  that  I  went  on  a  long  railroad  journey 
and  at  last  met  with  a  terrible  accident."  One  cannot 
doubt  that  the  catastrophe  was  the  dreamer's  interpreta- 
tion of  the  violent  extraction  of  a  tooth. 

The  dreaming  state  is  one  which  usually  has  little  or  no 
motor  expression.  Ellis  has  called  attention  to  the  fact 
that  in  dreams  we  may  either  think  that  we  move  with 
extraordinary  ease  and  speed,  or  we  may  have  the  sense 
of  inability  to  command  the  muscles.  Of  course,  the 
second  state  is  one  in  which  we  have  a  more  correct 
impression  of  the  actual  situation.  The  author  cited 
thinks  that  it  is  always  associated  with  shallow  sleep 
when  there  are  sensory  signs  of  the  immobility  of  the 
limbs.  With  deeper  sleep  these  signs  would  disappear 
and  the  dreamer  would  not  be  deterred  from  imagining 
remarkable  indulgences  in  locomotion  and  aviation. 

The  lack  of  brightness  in  the  ocular  sensations  possible 
to  one  with  closed  eyes  may  account  for  the  report  com- 
monly made  that  dream  scenery  is  colorless  and  sober. 
This  is  not  necessarily  the  case;  the  writer  often  ex- 
periences surprise  and  pleasure  when,  after  a  winter  day, 
he  finds  that  in  his  dream  country  the  grass  is  brilliantly 
green,  the  sky  intensely  blue,  and  the  sunshine  as  golden 
as  that  of  a  Sorolla  landscape.  It  is  generally  agreed 
that  sensations  of  taste  and  smell  are  rarely  noted  in 
dreams. 


CHAPTER   XVI 

CAUSES   OF   NERVOUS   IMPAIRMENT 

When  we  look  into  the  faces  of  men  and  women  as  we 
meet  them  on  the  street-cars  we  are  painfully  impressed 
with  the  widespread  prevalence  of  ill  health.  The  aver- 
n^c  expression  is  not  one  of  comfort,  hope,  and  good-will, 
l)ut  of  depression,  anxiet}^,  and  absorption  in  self.  The 
exceptional  face  which  is  radiant  of  strength  and  benevo- 
lence is  conspicuous  in  the  dreary  succession.  The  temp- 
tation is  to  pass  a  harsh  judgment  upon  those  who  seem 
so  unhappy  and  unfriendly  and  to  condemn  them  for  not 
being  otherwise.  Reflection  convinces  one  that  this  is 
unjust.  They  are  the  victims  of  heredity,  of  malnutrition, 
of  poverty,  and,  not  seldom,  of  voluntary  sacrifices.  It 
is  not  for  the  casual  spectator  to  say  how  far  they  are 
suffering  from  personal  dereliction  which  should  have 
been  avoided.  Whatever  the  past  facts  have  been,  the 
present  difficulty  with  most  of  these  people  is  imperfec- 
tion of  nervous  equipment. 

A  considerable  share  of  this  may  be  charged  to  neurotic 
inheritance.  Every  one  can  think  of  families  in  which 
nervous  instability  is  exemplified  in  various  forms  by  the 
different  members.  These  are  the  families  which  are 
given  to  quarreling  and  recrimination  at  home,  but  unite 
with  even  greater  pugnacity  against  the  outsider  who 
has  incurred  their  displeasure.  They  make  themselves 
miserable,  but  seem  unable  to  help  it.  Where  the  taint 
is  graver,  there  is  downright  neurasthenia.  From  such 
stock  come  certain  individuals  with  marked  talent,  but 
hampered  by  self-consciousness  and  excessive  sensitive- 
ness. The  temperament  is  not  a  modern  development, 
as  commonly  assumed,  but  as  old  as  the  time  of  Plato, 

192 


CAUSES    OF    NERVOUS    IMTAIRMIONT  193 

who  is  said  to  have  described  it  with  jj-reat  precision  and 
to  have  declared  such  persons  to  be  "undesirable  citi- 
zens" for  his  republic. 

But  the  proportion  of  people  who  fall  far  below  the 
normal  in  courage  and  perseverence,  in  kindliness  and 
contentment  is  too  large  to  allow  us  to  say  of  every  case 
that  the  inheritance  was  much  to  blame.  We  must  pass 
on  to  the  circumstances  affecting  the  individual.  These 
may  be  divided  into  those  which  are  strictly  physical  and 
those  which  can  be  described  as  unfortunate  mental 
habits.  Among  the  physical  factors  are  some  which  are 
bodily  and  some  which  are  environmental. 

We  may  conveniently  mention  first  disturbances  of 
nutrition.  The  opinion  is  commonly  held  that  many 
powerful  personahties  have  been  perverted  by  dyspepsia. 
This  is  said,  for  example,  of  Carlyle.  Of  course,  it  is  hard 
in  such  instances  to  say  which  is  cause  and  which  is  effect. 
The  indigestion  may  be  the  result  of  the  inefficiency  of  a 
nervous  system  in  which  pessimism  is  a  congenital  char- 
acteristic. This  is  a  difficulty  of  interpretation  which  we 
constantly  encounter  in  all  discussions  of  this  kind.  But 
whether  despondency  and  cynicism  are  primary  or  sec- 
ondary, there  is  no  reasonable  doubt  that  when  they  are 
once  estabhshed  they  continue  to  impair  the  digestive 
capacity,  and  the  alimentary  trouble  tends  to  intensify 
the  nervous  deficiency.  Thus,  we  have  an  illustration  of 
what  is  known  to  physicians  as  a  "vicious  cycle." 

The  reaction  of  a  disordered  stomach  and  intestine 
upon  the  brain  is  not  solely  by  means  of  nerve-impulses 
such  as  result  in  general  sensation.  It  is  now  believed 
that  the  influence  exerted  is  largely  due  to  chemical 
products  originating  in  abnormal  fermentation  processes 
in  the  canal.  Entering  the  blood,  these  deleterious  com- 
pounds are  borne  to  all  parts  of  the  body,  but  they  have 
an  especially  marked  effect  upon  the  central  nervous 
system.  The  condition  in  which  these  poisons  are  circu- 
lated and  become  productive  of  mischief  is  spoken  of  as 
auto-intoxication.     It  is  favored  by  overeating,  especially 

13 


194      THE    NERVOUS    SYSTEM    AND    ITS   CONSERVATION 

of  nitrogenous  foods  (meats,  eggs,  and  legumes).  But  it 
may  develop  also  when  the  diet  is  scanty,  for  it  has  become 
clear  in  recent  times  that  underfeeding  may  so  enfeeble 
the  reactions  of  the  organs  of  digestion  that  they  do  not 
care  for  tlie  food  so  well  as  they  would  for  a  larger  and 
more  stimulating  ration. 

Auto-intoxication  is  frequently  associated  with  anemia, 
and  this  condition — a  diminution  of  the  oxygen-carrying 
substance  in  the  blood — always  threatens  injury  to  the 
nervous  system.  It  implies  limited  endurance  in  every 
pursuit.  Just  how  the  anemia  of  auto-intoxication  is 
caused  is  not  always  plain.  In  some  cases  it  is  probably 
due  to  the  continuous  formation  in  the  intestine  of  a 
poison  which  is  destructive  to  the  red  c^jrpuscles. 

Among  the  bodil}^  sources  of  nervous  damage  we  do  well 
to  emphasize  eye-strain.  Attention  has  already  been 
called  to  the  primacy  of  the  eye  among  the  receptors 
through  which  the  organism  is  stimulated.  It  follows 
that  excessive  use  of  the  eyes  or  their  employment  under 
difficulties  must  be  harmful  in  a  high  degree.  A  little 
space  may  be  here  devoted  to  a  comparison  of  the  common 
visual  defects  as  causes  of  central  trouble.  The  normal 
eye  may  be  abused — as  by  reading  with  poor  light  or  in 
situations  where  there  is  vibration  (in  the  cars) — but  it  is 
of  special  importance  to  discuss  the  near-sighted,  the  far- 
sighted,  and  the  astigmatic  conditions. 

Near-sight  is  a  defect  ordinarily  referable  to  too  great 
depth  of  the  eyeball.  The  effect  upon  the  retinal  image 
is  the  same  that  is  produced  in  a  camera  when  the  dis- 
tance between  the  lens  and  the  plate  is  made  greater  than 
it  should  be  for  landscape  work.  The  distant  view  be- 
comes blurred  and  indistinct,  while  objects  at  short  range 
are  sharply  defined.  So  in  the  near-sighted  eye  no  clear 
picture  of  the  distance  is  obtainable,  but  things  close 
by  are  seen  with  a  minimum  of  effort.  What  is  called  the 
normal  eye  is  used  without  strain  for  observing  things  at  a 
distance,  and  applied  to  near  work  with  a  certain  sustained 
contraction   of   what  is   known   as   the   accommodation 


CAUSES    OF    NE-RVOUS    IMPAIRMENT  195 

muscle.  Moderate  near-sightedness  adapts  one  to  read 
or  sew  with  even  less  fatigue  than  if  the  eyes  were  strictly 
normal.  Nevertheless,  the  condition  has  serious  disad- 
vantages. 

If  a  child  is  at  all  near-sighted  it  may  be  predicted  that 
the  defect  will  grow  graver  during  the  period  of  school 
hfe.  The  actual  nervous  strain  involved  is  shght,  but  the 
indirect  results  may  be  deplorable.  The  boy  who  cannot 
see  well  at  a  distance  cuts  a  ludicrous  figure  in  vigorous 
outdoor  sport,  and,  being  subjected  to  ridicule,  abandons 
the  attempt  to  take  part  in  it.  At  first  he  is  sensitive  and 
aggrieved.  Later  he  convinces  himself  that  athletics  are 
not  worth  while  and  he  inchnes  to  become  a  bookworm, 
with  a  serious  lack  of  physical  stamina.  It  is  fortunate 
if  he  is  not  a  conceited  prig  in  the  bargain. 

Far-sight,  so  far  as  its  cause  is  concerned,  is  the  exact 
opposite  of  near-sight.  The  eyeball  is  not  deep  enough. 
A  simple  experiment  with  a  camera  will  serve  to  show  that 
such  a  relationship  between  lens  and  screen  will  result  in  a 
failure  to  focus  anything  sharply,  though  the  distance  will 
be  better  imaged  than  the  foreground.  By  an  effort  such 
as  one  with  normal  vision  makes  to  see  objects  nearby, 
the  far-sighted  person  secures  clear  vision  for  distance;  to 
read  or  do  other  close  work  he  must  subject  the  accommo- 
dation muscle  to  an  additional  strain.  Thus,  his  eyes  are 
never  at  rest  when  they  are  being  used  at  all.  Yet  he  can 
see  quite  well  anything  to  which  he  turns  his  attention, 
and  it  may  be  hard  to  make  him  accept  the  fact  that  he 
has  a  visual  defect  calling  for  glasses.  Headaches,  indi- 
gestion, and  general  nervous  disturbances  may  result 
from  this  condition. 

Regular  astigmatism  is  an  imperfection  of  the  cornea  or 
anterior  surface  of  the  eye.  In  the  majority  of  cases  the 
trouble  is  an  excess  of  curvature  up  and  down  as  com- 
pared with  that  from  right  to  left.  This  has  been  well 
described  as  spoon-shaped  cornea;  in  geometric  temis 
this  important  refracting  surface  of  the  eye  is  ellipsoid 
instead    of    spheric.      The    purely    optical    consequences 


19(3      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

need  not  be  set  forth;  the  word  "astigmatism"  means 
Hterally  "not  pointedncss,"  and  the  reference  is  to  the  fact 
that  with  such  curvatures  a  point  outside  can  never  be 
imaged  as  a  point  upon  the  retina.  Vision  can  never  be 
satisfactory,  but  at  a  given  moment  certain  Hnear  features 
of  the  scene  will  be  clearer  than  others  which  have  a  dif- 
ferent direction.  The  attempt  to  change  the  degree  of 
accommodation  so  as  to  have  a  better  definition  for  the 
second  set  of  lines  results  in  sacrificing  the  sharpness  of  the 
first.  Hence,  there  is  a  restless  flutter  of  the  accommoda- 
tion mechanism,  a  perpetual  attempt  to  gain  a  compre- 
hensive view,  which  is  destined  always  to  be  baffled. 

The  effects  of  common  astigmatism  ui3on  health  are 
much  like  those  of  far-sight.  The  glasses  used  to  correct 
the  deficiency  must  themselves  be  astigmatic,  but  in  a 
sense  opposite  to  that  in  the  eyes  to  which  they  are  added. 
They  must  have  their  least  curvature  in  the  meridian  in 
which  the  cornea  has  its  greatest.  The  mounting  of  such 
lenses  is  evidently  a  matter  of  importance,  for  there  is 
only  one  position  in  which  they  can  fulfil  their  purpose. 

Sound  heredity,  successful  nutrition,  and  eyes  free  from 
hurtful  strain  go  far  toward  securing  an  efficient  nervous 
system,  but  we  have  yet  other  factors  to  reckon  with. 
All  bodily  conditions  which  cause  discomfort  must  be 
regarded  as  possible  sources  of  central  injury.  It  is  prob- 
able, moreover,  that  many  peripheral  derangements  which 
we  think  we  can  ignore  or  which  may  even  have  escaped 
our  recognition,  may  be  productive  of  much  harm.  We 
have  seen  that  this  is  true  of  far-sight.  An  eminent 
surgeon,  G.  W.  Crile,  has  furnished  striking  evidence  that 
this  may  be  frequently  a  fact.  The  foundation  of  his 
exposition  is  the  body  of  information  we  possess  with 
respect  to  anesthesia.' 

When  ether  or  chloroform  is  introduced  into  the  blood 
and  carried  to  the  brain  there  is  an  interruption  of  certain 
processes  in  the  neurons  which  modifies  or  destroys  con- 
sciousness, but  we  have  no  warrant  for  assuming  that 
1  Boston  Medical  and  Surgical  Jom-nal,  1910,  clxiii,  892. 


CAUSES    OF   NERVOUS   IMPAIRMENT  197 

ordinary  anesthesia  suspends  all  the  many  central  activi- 
ties. In  fact,  we  know  that  it  does  not,  for  it  would  be  fatal 
if  it  did.  The  presumption  is  that  certain  synapses  arc 
much  more  easily  affected  than  others,  whence  it  follows 
that  we  can  subdue  cortical  currents  to  a  considerable 
extent  without  paralyzing  the  respiratory  center.  Now, 
it  is  the  belief  of  Crile  that  when  an  operation  is  con- 
ducted under  ether  or  chloroform,  streams  of  impulses 
ascend  to  the  brain  from  the  seat  of  the  cutting  and 
cauterizing.  These  would  produce  terrible  pain  in  the 
conscious  subject  and  reflex  struggHng  of  the  most  desper- 
ate intensity.  In  the  actual  case  the  pain  is  avoided  and 
the  reflexes  are  greatly  reduced.  But  are  we  to  suppose 
that  the  afferent  impulses  are  wholly  without  effect  upon 
the  brain?  Crile  contends  that  they  continue  to  work 
injury  to  the  central  gray  matter  even  in  the  absence  of 
consciousness  and  reflexes. 

Experimental  evidence  has  been  secured  by  making 
microscopic  studies  of  the  brain  tissue  in  animals  which 
have  undergone  severe  operations  under  the  common 
anesthetics.  Cellular  changes  are  described  which  are 
of  the  same  nature  as  those  long  held  to  denote  profound 
fatigue.  Such  alterations  are  not  seen  in  the  brains  of 
animals  which  have  merely  been  etherized  for  a  long  time 
without  operation.  Hence,  Crile  refers  them  to  the  inflow 
of  impulses  from  the  parts  that  have  been  so  powerfully 
stimulated. 

All  this  may  seem  to  be  a  technical  digression,  but  we 
shall  find  that  it  opens  certain  considerations  of  the  most 
practical  kind.  It  will  be  noted  that  the  central  fact  in 
Crile's  thesis  is  this:  Sensation  does  not  constitute  a 
reliable  measure  of  the  damage  done  to  the  nervous  sys- 
tem by  afferent  currents.  To  disregard  a  source  of  such 
impulses  is  not  to  nullify  their  influence.  It  is  always 
better  to  remove  the  cause  than  to  seek  to  suppress  the 
cerebral  echo.  Using  a  text  Uke  this,  we  msiy  indict 
the  principles  of  psychotherapy  under  any  of  its  various 
names  when  it  seeks  to  treat  organic  disease.     It  under- 


198      THK    XERVOUS    SYSTK.M    AND    ITS    CONSERVATION 

takes  to  abolish  pain,  and  this  it  may  do  willi  surprising 
success.  But  this  is  a  species  of  narcosis  and  carries  with 
it  no  certain  assurance  that  the  nervous  system  is  not  to 
suffer  progressive  injury  from  the  sulx'onscious  stimula- 
tion. 

This  criticism  should  not  be  launched  without  giving 
larger  recognition  to  the  usefulness  of  psychotherapeutic 
measures,  even  where  the  trouble  is  an  organic  one. 
Freedom  from  pain  favors  sleep  and  nutrition.  Hence, 
it  may  easily  prove  to  be  the  only  condition  which  is 
needed  to  initiate  a  recovery.  Again,  the  banishment  of 
pain  is  always  beneficent  when  the  disease  is  incurable. 
But  when  the  peripheral  cause  of  distress  can  be  corrected, 
it  is  always  better  to  attend  to  it. 

One  can  readily  think  of  a  rather  large  number  of 
ph^^sical  lesions  which  are  apt  to  be  tolerated  or  even  for- 
gotten which  are  possil^le  sources  of  injurious  stimulation. 
Defective  teeth  afford  an  example.  Many  troubles  asso- 
ciated with,  the  feet,  such  as  corns,  broken  arches,  or  even 
badly  fitted  shoes,  belong  in  the  same  class.  Nasal  ob- 
structions may  have  the  same  influence.  Hemorrhoids 
and  uterine  displacements  are  more  serious  conditions 
and  have  a  like  tendency,  only  more  obviously  effective. 
Surgical  operations  for  the  relief  of  such  conditions  may 
bring  about  what  is  little  less  than  a  regeneration  of  the 
character  of  the  individual.  Among  temporary  causes 
of  imperfectly  realized  nervous  strain  may  be  mentioned 
the  wearing  of  orthodontia  appliances.  Children  obliged 
to  submit  to  these  instruments  may  not  complain  of  great 
distress,  but  they  are  likely  to  be  made  irritable  and  tired  by 
the  constant  wear  and  tear.  An  additional  factor  in  some 
cases  is  found  in  the  loss  of  pleasure  in  eating  which  the 
apparatus  is  likely  to  entail. 

A  word  of  criticism  may  be  introduced  here  regarding 
current  views  concerning  ventilation.  The  simple  and 
summary  doctrine  prevails  that  air  cannot  be  bad  unless 
it  is  too  warm.  The  odors  by  which  we  usually  gage  the 
success  or  failure  of  a  system  are  lightly  treated.     It  is 


CAUSES   OF    NERVOUS    IMPAIRMENT  199 

said  that  we  soon  cease  to  perceive  them,  and  that,  there- 
fore, they  do  not  signify  anything  of  moment.  Is  this  not 
a  dangerous  assumption?  An  odor  is  the  sign  of  a  chem- 
ical agent  working  upon  the  nervous  system;  we  have  no 
right  to  say  that  this  agent  has  ceased  to  act  when  we  have 
ceased  to  feel  its  immediate  effects.  Such  a  claim  is  equiv- 
alent to  the  assertion  that  nothing  can  influence  a  sleeper 
unless  it  wakes  him. 

Less  attention  is  usually  paid  to  the  bodily  sources  of 
nervous  impairment  such  as  we  have  been  discussing  than 
to  the  influence  of  occupation,  surroundings,  and  the 
mental  life.  Nervous  break-downs  are  most  frequently 
attributed  to  overwork.  But  according  to  the  judgment 
of  the  ablest  specialists  work  in  itself  is  not  often  the  sole 
cause  of  these  disasters.  Work  may  be  hard  and  fatiguing, 
but  if  it  is  congenial  and  at  all  successful,  if  it  does  not 
encroach  upon  the  hours  of  sleep,  and  if  it  is  not  a  subject 
of  anxiety  which  the  worker  cannot  easily  dismiss,  it  is 
not  likely  to  do  him  harm.  If,  on  the  other  hand,  the 
work  involves  worry  and  discouragement,  if  it  so  fills 
the  mind  that  it  cannot  be  put  aside  at  will,  it.  does  become 
a  menace  to  the  poise  and  efficiency  of  the  nervous  system. 

If  work  is  of  an  unwelcome  kind  and  is  performed  in  a 
rebellious  spirit,  so  much  the  worse  for  the  subject.  The 
question  may  be  asked:  What  of  the  mill-operatives,  with 
their  monotonous  and  uninteresting  ta.sks,  are  they 
particularly  subject  to  nervous  disease?  One  would  at 
first  say  that  they  must  be  so,  but  there  are  certain  fac- 
tors which  favor  their  protection  against  it.^  They  are 
not  obliged  to  think  of  their  work  at  all  beyond  the  hours 
assigned  to  it.  Unless  they  are  doing  piece-work  they 
have  no  ambition  to  increase  speed.  Moreover — and  this 
is  a  very  important  point — they  do  not  have  at  short  in- 
tervals to  make  choices  between  different  duties  which  de- 
mand attention.  There  is  a  restful  element  in  having  but 
one  definite  thing  to  do  and  being  freed  from  the  anxiety 

^But  see  Goldmark,  "Fatigue  and  Efficiency,"  New  York  Chari- 
ties Publication  Committee,  1912. 


200      THE    XERVOIS    SYSTEM    AM)    ITS    CONSERVATION 

lest  some  other  matter  should  have  had  the  precedence. 
The  sense  of  being  pressed  by  numerous  concerns  of  nearly 
equal  urgency  is  pro]>ably  a  root  of  much  evil  in  the  Ufe 
of  the  "careful  and  troubled"  housewife. 

The  clash  of  antipathetic  i-)ersonalitics  is  a  most  serious 
element  among  the  causes  of  nerve-fag.  It  is  one  which 
becomes  steadily  more  potent  for  injury  when  a  certain 
measure  of  fatigue  has  arrived,  for  added  irritability  means 
more  and  more  grievous  friction.  It  is  a  rare  family  in 
which  the  atmosphere  is  not  improved  by  temporary  sepa- 
ration of  the  house-mates.  The  entertaining  of  visitors 
serves  a  good  purpose  when  the  guests  absorb  attention 
that  would  otherwise  be  bestowed  exclusively  upon 
members  of  the  home  circle  and  in  a  critical  spirit.  It  is  a 
lamentable  fact  that  in  most  families  there  is  more  restraint 
in  speech  and  more  consideration  in  conduct  when  out- 
siders are  present;  this  suggests  another  valuable  service 
rendered  by  company.  Neurasthenia  is,  in  a  certain  sense, 
a  contagious  disease:  one  case  fully  developed  may  give 
rise  to  others,  though  the  secondary  ones  are  ordinarily 
less  severe. 

Some  one  has  shrewdly  pointed  out  that  one  fruitful 
source  of  mischief  in  the  nervous  system  consists  in  what 
may  be  succinctly  described  as  not  minchng  one's  own 
business.  People  easily  fall  into  the  habit  of  fretting  over 
the  beliefs  and  the  behavior  of  their  associates  in  matters 
in  which  individual  liberty  ought  to  l:>e  respected.  Among 
the  uneducated  this  results  in  the  attempt  to  dictate,  and 
futile  contention  follows.  Higher  in  the  social  scale  a  man 
or  woman  who  commits  this  error  may  not  be  so  aggressive, 
but  will  brood  unhappily  over  the  principles  or  actions  held 
in  such  strong  disapproval.  It  is  nmch  better  not  to  be 
the  "brother's  keeper"  unless  the  interest  is  clearly  philan- 
thropic. Why  should  a  man  distress  himself  because  a 
fellow-being  is  fond  of  cheese,  which  he  does  not  like?— 
or  goes  to  church,  which  he  does  not  wish  to  do?  It  is 
sound  hj'giene  to  live  and  let  live.  The  world,  indeed, 
needs  reformers,  but  their  task  is  one  which  calls  for  so 


CAUSES    OF    NERVOUS    IMPAIRMENT  201 

much  personal  sacrifice  that  they  should  be  sure  the  cause 
is  worthy  of  the  expenditure.  A  sense  of  humor  is  a  sav- 
ing grace  for  those  in  whom  the  impulse  to  regulate  the 
lives  of  others  is  a  powerful  one. 

Let  us  summarize  the  conditions  we  have  named  as 
helping  to  maintain  the  nervous  system  in  a  normal 
state  and  so  to  keep  the  individual  happy  and  efficient. 
We  have  recognized  that  a  sound  inheritance  goes  far  to 
secure  this  end.  Any  neurotic  tendency  of  the  stock  is  a 
handicap  and  makes  it  the  more  imperative  that  other 
unfavorable  influences  shall  be  avoided.  Physical  defects 
are  to  be  corrected  wherever  possible,  even  though  it  may 
seem  easy  to  put  up  with  them.  Environmental  factors, 
such  as  fresh  air,  well-regulated  illumination,  and  quiet  for 
the  hours  of  sleep,  must  receive  attention.  A  moderate 
but  not  a  harassing  variety  of  occupation  and  thought  is 
to  be  recommended.  And  no  responsibility  which  it  is 
not  clearly  a  duty  to  bear — no  gratuitous  anxiety — is  to 
be  assumed. 

Sometimes  people  exhaust  themselves  in  what  is  judged 
to  be  purely  unselfish  and  sacrificing  devotion.  To  such 
it  may  be  necessary  to  say  that  future  as  well  as  present 
usefulness  must  be  considered.  The  sum  total  of  service 
that  can  be  rendered  to  the  family  or  other  associates  is 
likely  to  be  greater  when  there  is  some  deliberate  sparing 
of  one's  self,  some  reservation  of  time  for  rest  and  recrea- 
tion, than  when  the  offering  of  labor  and  sympathy  is 
absolutely  unsparing.  Of  course,  there  are  exceptional 
crises  when  any  thought  of  self  would  be  base,  but,  as  a 
rule,  the  greatest  contribution  can  be  made  by  those  who 
practise  a  wise  conservation  of  their  resources. 

Reference  must  be  made  once  more  to  the  inestimable 
value  of  the  Seventh  Day  for  the  preservation  of  the  ner- 
vous system.  The  deepest  degradation  to  which  the 
Sabbath  can  be  subjected  is  to  fill  it  with  odd  jobs  left 
over  from  the  week's  routine.  The  compulsions  of 
Sunday  should  be  from  within,  not  from  without.  So  far 
as  possible  the  day  should  bring  complete  release  from 


202    THE  np:rvois  system  and  its  conservation 

habitual  petty  cares  and  scope  for  the  icleaUstic  Ufe. 
A  certain  parallel  may  be  suggested  between  the  renewing 
function  of  the  Sal)bath  and  the  benefit  to  the  eyes  that 
proceeds  from  relaxing  the  muscle  of  accommodation. 
We  necessarily  bestow  much  of  our  attention  upon  objects 
close  at  hand  and  rapidly  changing.  We  rest  our  eyes  by 
looking  away  to  the  mountains  with  their  unvarying  out- 
lines. So  the  nervous  system,  after  making  its  swift 
adaptive  changes  to  meet  the  innumerable  little  exigen- 
cies of  the  six  days,  may  well  be  permitted  on  the  seventh 
to  find  a  profoundly  restful  relation  to  "the  things  which 
are  not  seen." 


CHAPTER  XVII 
NEURASTHENIA 

In  the  previous  chapter  we  have  attempted  to  catalog 
some  of  the  factors  which  tend  to  subject  the  nervous  sys- 
tem to  gradually  deepening  injury.  We  have  now  to  de- 
vote some  space  to  the  ways  in  which  this  injury  is  usually 
manifested.  "Nervous  fatigue,"  ''nerve  fag,"  "nervous 
prostration,"  "nervous  exhaustion" — these  are  expressions 
used  to  denote  different  degrees  of  a  condition  which  is 
covered  by  the  word  "neurasthenia. "^  It  is  an  example  of 
what  is  called  a  "functional  disorder."  By  this  term 
physicians  characterize  diseases  in  which  no  structural 
change  in  the  tissues  can  be  demonstrated  postmortem. 
Ordinary  neurasthenia  is  thus  brought  into  contrast  with 
those  perversions  of  nervous  reaction  which  are  caused  by 
obvious  abnormalities  of  the  brain — paralyses,  manias, 
epilepsies,  etc.,  due  to  hemorrhages,  tumors,  infections,  and 
the  like.  The  adjective  organic  is  the  one  chosen  to  set 
over  against  the  term  "functional." 

The  distinction  between  functional  and  organic  troubles 
is  often  a  helpful  one,  but  it  may  be  criticized  as  unscien- 
tific. There  is  a  medical  maxim  which  says,  "There  is  no 
psychosis  without  a  neurosis,"  that  is,  the  nervous  system 
will  not  act  in  an  abnormal  way  unless  it  is  physically 
abnormal.  All  its  disorders  are,  therefore,  organic  in  the 
best  sense,  and  a  functional  disease  is  a  fiction.  All  that 
can  be  claimed  for  the  so-called  functional  disturbances  is 
that  the  derangement  is  chemical  rather  than  structural, 
molecular  rather  than  molar.  It  follows,  however,  that 
recovery  is  much  more  probable  in  the  functional  cases. 

^  The  word  is  often  restricted  to  cases  of  a  certain  t5T)e.  It  is 
here  used  more  inclusively,  but  in  a  way  which  does  no  violence  to 
the  root  meaning. 

203 


204      THE    NERVOUS    SYSTKM    A.\D    ITS    CONSKUVATION 

If  a  layman  is  to  enter  at  all  upon  a  theme  which  properly 
belongs  to  the  practitioner,  he  should  cite  the  authority 
from  which  ho  draws  most  freely.  The  chief  source  of  the 
folk)wino;  account  is  Courtney's  "The  Concjuest  of  Nerves."  ^ 
The  book  can  be  connnended  to  all  who  seek  an  analj^sis 
of  neurasthenia  at  once  scientific  and  sympathetic,  with 
many  sane  suggestions  for  its  relief.  The  same  author  has 
contributed  the  section  on  the  nervous  system  in  Pyle's 
"Personal  Hygiene,"  -  where  a  more  condensed  presenta- 
tion of  similar  material  may  be  found. 

The  nervous  system  seems  to  suffer  from  fatigue  of  two 
orders.  First,  there  is  that  which  may  be  called  the  daily 
tj'pe,  from  which  complete  recover}^  occurs  in  the  course 
of  a  night's  sleep.  This  has  been  sufficient^  discussed  (see 
Chapter  XII).  Another  type  of  fatigue  is  that  which  is 
cumulative  from  day  to  day,  and  which  cannot  be  quickly 
compensated.  It  results  from  the  coexistence  of  some 
or  all  the  factors  mentioned  in  the  last  chapter,  and  when 
it  is  far  enough  developed  it  is  recognized  as  neurasthenia. 
There  is  a  single  principle  which  proves  to  be  the  key  to 
the  problem:  it  is  the  fact  that  in  nervous  fatigue  of  the 
central  order  there  is  a  large  element  of  hypersensitiveness 
and  consequent  excessive  activity. 

We  usually  think  of  fatigue  as  a  distinct  depression  of 
capacity  for  action.  This  is  true  in  a  general  way  of  the 
neuromuscular  system,  though  even  with  the  simplified 
conditions  of  laboratory  trials  it  has  been  shown  that  a 
moderate  amount  of  contraction  increases  the  working 
power  of  muscle.  Lee  has  interpreted  this  as  meaning 
that  the  metabolic  products  of  the  contractile  process, 
the  same  compounds  which  in  larger  quantities  will  limit 
the  performance  of  the  mechanism,  act  at  first  as  stimu- 
lants. This  seems  to  be  much  more  distinctly  the  case 
with  the  neurons  of  the  brain  and  cord. 

We  can  often  observe  in  people  tired  by  a  day  of  excite- 
ment— perhaps  of  sightseeing— that  there  is  an  appear- 

1  Macmillan,  New  York,  1911. 

^  W.  B.  Saunders  Co.,  Philadelphia. 


NEURASTHENIA  205 

ance  of  stimulation.  They  are  talkative  and  demonstra- 
tive. They  laugh  easily  and  with  abandon.  Their  state 
suggests  a  mild  intoxication.  It  may  be  that  the  condi- 
tion is  more  like  an  intoxication  than  we  should  be  in- 
clined to  think.  We  account  for  the  garrulity  of  banquet- 
ers by  saying  that  the  alcohol  has  acted  as  a  narcotic, 
selecting  the  inhibitory  centers  for  its  primary  action  and 
so  giving  the  outward  and  subjective  signs  of  stimulation. 
The  influence  of  the  fatigue  substances  upon  the  brain 
may  be  much  like  this.  Whether  the  secret  of  the  in- 
fluence consists  in  a  general  stimulation  or  in  the  with- 
drawal of  desirable  inhibitions,  the  obvious  result  is  aug- 
mented activity. 

Once  before  we  have  alluded  to  the  fact  that  the  tired 
nervous  system  craves  employment,  though  it  needs 
repose.  Many  people  will  appreciate  the  following  in- 
stance cited  by  J.  J.  Putnam:  An  overwrought  woman 
had  appealed  to  an  old  physician  for  advice.  He  had  told 
her  that  she  must  rest.  Her  reply  was  that  she  did  not 
feel  tired  and  could  not  bring  herself  to  be  still.  ''Madam," 
said  the  doctor,  "you  will  have  to  lie  down  until  you  are 
tired  and  then  rest."  A  hyperexcitability  like  this  is  un- 
happily common  in  children,  who  nowadays  have  less 
training  in  the  exercise  of  inhibition  than  fell  to  the  lot 
of  earlier  generations.  We  may  now  go  on  to  see  how  con- 
sistently the  neurasthenic  exemplifies  this  heightened 
nervous  activity  in  every  department  of  his  organization. 
It  is  easy  to  recognize  that  a  vicious  cycle  is  involved, 
the  overaction  intensifying  the  fatigue  and  yet  failing  to 
bring  automatic  relaxation. 

Guided  by  Courtney,  we  shall  consider  the  signs  of 
neurasthenia  as  they  appear  in  four  realms.  These  are: 
(1)  The  motor  mechanism,  (2)  the  sensory  equipment, 
(3)  the  autonomic  or  visceral  field,  and  (4)  the  tempera- 
ment. The  connections  of  all  these  are  such  that  dis- 
turbances in  one  must  be  expected  to  overflow  upon  the 
others.  The  reflex  principle  makes  this  inevitable.  In 
order  that  an  organism  shall  be  properly  adjusted  to 


200      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

its  normal  environment  its  central  nervous  system  must 
have  a  medium  degree  of  resistance  to  the  transmission 
of  impulses.  If  the  resistance  is  raised,  as  by  anesthesia, 
the  result  is  too  great  inertia;  if  the  resistance  is  unduly 
lowered,  there  are  wasteful  and  exhausting  reactions  in 
response  to  stimuli  which  might  as  well  have  failed  to 
produce  any  discharge  of  energy. 

1.  In  the  realm  of  the  skeletal  muscles  nervous  fatigue 
expresses  itself  in  the  familiar  form  of  restlessness.  The 
victim  has  less  than  his  usual  endurance  and  may  be  con- 
sciously tired  by  his  own  unprofitable  activity,  but  he 
cannot  keep  still.  He  crosses  and  uncrosses  his  legs, 
fum})les  with  his  watch-chain,  twirls  his  moustache,  walks 
about  aimlessly,  and  tries  one  chair  after  another.  Court- 
ney has  acutely  noted  the  predilection  of  the  neurasthenic 
for  rockers,  which  give  an  outlet  to  his  uneasiness.  In 
some  sanitariums  the  trouble  is  attacked  along  this  fine; 
hard  and  simple  manual  work  is  prescribed  and  pushed  to 
the  point  of  weariness,  that  primitive  exhaustion  which 
is  pleasant  by  contrast  with  the  other  and  which  brings 
sleep  as  its  reward. 

2.  The  sensory  symptoms  are  just  what  we  might  expect 
if  the  central  characteristic  is  one  of  lowered  resistance. 
Stimuli  which  are  not  noticed  by  one  in  health  are  felt 
unpleasantly,  and  sensations  readily  ignored  by  the  normal 
man  become  torment.  This  is  true  for  the  cutaneous  sen- 
sations; the  neurasthenic  is  dissatisfied  with  the  feeling 
of  his  clothes  and  his  bed.  He  is  morbidly  sensitive  to 
changes  of  temperature.  When  others  would  say  merely' 
that  the  room  had  grown  a  trifle  warm,  he  says  that  it  is 
unbearably  hot.  When  it  is  really  a  little  cooler  than  is 
ideal,  he  feels  thoroughly  chilled.  He  is  much  affected 
by  all  changes  of  weather  and  may  conceive  an  aversion 
for  certain  winds,  proving  his  keenness  of  judgment  by 
announcing  each  change. 

The  eyes  share  the  general  supersensitiveness.  Strong 
light  is  objectionable  and  the  shrinking  from  it  may  grow 
into  photophobia.    The  after-images,  those  spots  of  com- 


NEURASTHENIA  207 

plementary  color  which  anyone  may  observe  after  looking 
fixedly  at  bright  objects,  become  persistent  and  dis- 
quieting. The  entoptic  appearances,  the  shreds  and  spots 
in  the  humors  of  the  eye  and  the  twinkling  corpuscles  in 
the  capillaries  of  the  retina,  obtrude  themselves  upon  the 
attention.  Johannes  Miiller  was  at  one  time  greatly  dis- 
tressed by  the  loss  of  the  power  to  exclude  these  things 
from  his  consciousness.  They  may  be  seized  upon  as 
symptoms  of  ocular  or  brain  disease. 

As  it  is  with  the  eye,  so  it  is  with  the  ear.  Sounds  be- 
come wearisome;  sometimes  the  loud  ones  are  particularly 
irritating,  so  that  the  subject  cannot  bear  to  hear  children 
at  play,  sometimes  the  greatest  annoyance  proceeds  rather 
from  sUght  and  repeated  noises,  hke  the  ticking  of  a  clock 
or  the  gnawing  of  a  mouse  within  the  bedroom  wall. 
Olfactory  stimuli  may  have  an  intensified  effect  and  the 
detestation  of  certain  odors  may  seem  unreasonable. 
The  sensory  relations  of  the  neurasthenic  should  serve 
to  make  clear  to  a  well  person  how  desirable  it  is  to  be  pro- 
tected against  so  many  of  these  possible  sources  of  dis- 
comfort by  the  height  of  the  normal  "threshold."  The 
same  external  forces  assail  the  vigorous  and  the  weakened 
subjects  ahke,  but  the  sufferer  from  nervous  fatigue 
is  like  a  man  without  a  cuticle — everything  is  felt  too 
keenly. 

3.  As  the  admission  of  impulses  into  the  central  fabric 
is  too  free,  so  the  outpouring  that  follows  is  too  profuse. 
We  have  seen  how  this  is  expressed  through  the  neuro- 
muscular system  as  unrest.  We  have  now  to  turn  to  the 
autonomic  system.  Impulses  sent  out  over  the  paths  of 
this  system  may  have  either  inhibitory  or  excitatory 
effects.  We  find  evidence  of  their  action  upon  the  heart, 
the  blood-vessels,  the  digestive  tract,  the  genito-urinary 
organs,  and  the  sweat-glands.  The  list  might  readily  be 
extended  to  include  still  other  responding  elements. 

Heart  symptoms  in  the  neurasthenic  are  common. 
They  may  be  due  in  part  to  the  direct  flow  of  impulses  of 
undesirable  intensity  from  the  medulla  to  the  organ;  they 


208      THE    NERVOUS    SYSTEM    AXD    ITS    CONSERVATION 

are  xcvy  lik(>ly  to  be  aujijinciited  by  rcHox  influences  from 
a  disordered  alinientar}^  canal.  Irregularities  of  the 
heart-beats  are  likely  to  be  noticed  and  there  are  uneasy 
sensations  of  abnormal  mobility  about  the  heart,  feelings 
"as  though  it  turned  over,"  etc.  The  acceleration  during 
muscular  activity  may  seem  greater  than  it  should  be 
and  the  ^'ictim  may  become  fearful  of  local  organic  defects. 
Along  with  the  cardiac  misbehavior  thei'e  will  probably  be 
vasomotor  instability.  It  is  the  duty  of  the  vasomotor 
system  to  maintain  a  proper  and  nearly  steady  arterial 
pressure.  Failure  to  do  this  may  result  in  feelings  of 
faintness  and  vertigo,  perhaps,  at  other  times,  in  head- 
ache. 

To  the  perverted  action  of  the  vasomotor  system  we  may 
ascribe  the  exaggerated  judgments  of  warmth  and  cold 
already  mentioned.  If  the  nervous  mechanism  is  in  such 
a  "hair-trigger"  condition  that  a  slight  rise  of  the  external 
temperature  causes  an  intense  flushing  of  the  skin,  while  a 
slight  depression  renders  it  anemic,  these  impressions  are 
to  be  expected.  It  is  to  be  remembered  that  the  tempera- 
ture which  we  feel  is  that  of  the  skin  and  not  that  of  the  air. 
The  waxing  and  waning  of  the  cutaneous  blood-flow  will 
have  as  much  to  do  with  the  sensation  as  the  state  of  the 
air  outside.  In  the  neurasthenic  the  vasomotor  changes 
which  accompany  emotion  are  excessive.  Extraordinary 
outbreaks  of  perspiration  are  frequent. 

The  symptoms  arising  from  the  functional  derangement 
of  the  alimentary  canal  are  of  especial  importance.  It 
was  stated  in  an  earlier  chapter  that  this  essential  system 
has  such  a  degree  of  automaticity  that  in  many  cases  it 
might  work  better  with  no  intercourse  with  the  brain  and 
cord  than  it  is  actually  observed  to  do.  Foster  speaks  of 
the  improvement  of  digestive  capacity  often  noted  in  the 
aged.  As  the  nerve-centers  become  less  dominant  the 
stomach  and  intestine  do  their  duty  in  a  more  reliable 
manner  than  they  did  under  more  constant  regulation, 
and  the  former  dyspeptic  "eats  with  the  courage  and 
success  of  a  boy."     In  view  of  such  facts  we  can  under- 


NEURASTHENIA  209 

stand  that  the  organs  of  digestion  in  the  neurasthenic  are 
suffering  from  too  much  intermeddUng. 

The  central  influence  is  so  largely  inhibitory  that  the 
chief  effect  may  be  characterized  as  a  general  retardation 
of  the  activities  of  the  tract.  This  includes  a  loss  of  posi- 
tiveness  in  movement  and  a  withholding  of  secretions. 
The  stomach  retains  its  contents  longer  than  it  should,  and 
instead  of  being  acted  upon  by  a  strong  and  antiseptic 
gastric  juice,  they  are  fermented  by  micro-organisms. 
What  happens  in  the  stomach  is  continued  with  minor 
variations  in  the  intestine.  The  extensive  decomposition 
may  well  give  rise  to  definitely  poisonous  bodies  and  so 
to  auto-intoxication,  which  is  thus  both  a  cause  and  an 
effect  of  neurasthenia.  Another  annoying  result  of  the 
fermentation  is  the  voluminous  production  of  gas.  This 
feature  of  nervous  prostration  is  so  marked  that  some 
physicians  have  thought  that  the  quantity  of  the  gas  could 
not  all  be  due  to  bacterial  action.  They  have  considered 
whether  it  might  not  come  in  part  from  an  actual  .secre- 
tion of  carbon  dioxid  from  the  blood  into  the  tract.  At 
any  rate,  it  becomes  a  source  of  discomfort,  even  of  sharp 
pain,  while  the  distention  is  likely  to  occasion  reflex  dis- 
turbances of  heart  action.  The  picture  is  a  familiar  one, 
particularly  in  the  country,  where  there  is  less  thought 
for  appearances — the  sallow,  angular  dyspeptic,  with  fre- 
quent sighs  and  yawns  and  noisy  belching  of  gas. 

With  deficient  tone  and  peristalsis,  constipation  is  to  be 
anticipated.  It  may  be  extreme  and  is  a  matter  much 
brooded  over  by  the  sufferer.  He  may  be  much  given  to 
experimenting  with  cathartics  and  enemata.  On  the 
other  hand,  constipation  may  actually  exist  and  yet  be 
unrecognized,  for,  if  there  are  massive  accumulations  in 
the  colon  which  the  relaxed  muscles  fail  to  displace,  the 
local  irritation  may  set  up  a  catarrhal  condition  with 
liquid  discharges  made  urgent  by  the  ever-present  gas 
and  simulating  diarrhea.  There  are  two  places  in  the 
large  intestine  where  fecal  retention  is  likely  and  which 
may  become  the  seat  of  pain.     One  is  near  the  spleen 

14 


210      THE    NERVOUS    SYSTEM    AND    ITS   CONSERVATION 

(close  to  the  lower  ribs  on  the  left  side)  and  the  other  is  at 
the  sigmoid  flexure  lower  down  on  the  same  side.  Severe 
pain  is  said  to  arise  from  the  overloaded  sigmoid  and  to  be 
referred  to  the  left  groin  and  hip-joint. 

These  various  pains  are  not  readily  attributed  by  the 
neurasthenic  to  their  ignoble  and  commonplace  cause.  He 
is  half-anxious  to  find  grounds  for  the  belief  that  he  is 
suffering  from  a  mortal  disease,  and  he  prefers  the  idea 
of  a  cancer  to  constipation  of  nervous  origin.  Courtney 
says  incisively  that  his  fears  lead  only  to  an  anticlimax — 
he  is  very  likely  to  develop  hemorrhoids. 

The  genito-urinary  tract  does  not  escape  the  influ- 
ences of  the  overactive  centers.  The  concentration  of 
the  urine  varies  in  an  erratic  way  between  extremes. 
When  it  is  scanty  and  high  colored,  depositing  sediment 
on  standing,  the  subject  may  diagnose  his  case  as  Bright's 
disease.  If,  a  little  later,  it  becomes  pale  and  profuse, 
he  may  decide  that  he  has  diabetes.  There  is  plenty  of 
pernicious  advertising  matter  to  confirm  any  of  his  con- 
clusions. The  bladder  is  hkely  to  be  irritable  and  micturi- 
tion frequent.  The  reactions  of  the  reproductive  organs 
come  in  for  a  share  of  anxious  surveillance,  especially  in 
the  young.  Here,  even  more  than  with  the  kidneys,  the 
insidious  suggestions  of  quacks  sent  broadcast  in  their 
repulsive  literature  may  stimulate  agonies  of  fear. 

4.  Many  glimpses  of  the  subjective  state  in  neurasthenia 
have  already  been  afforded.  It  is  one  of  egotism,  disregard 
of  others,  and  self-pity.  We  have  most  of  us  reason  to 
cherish  memories  of  men  and  women  who  have  gone  with 
splendid  heroism  and  unselfishness  through  seasons  of 
suffering  and  even  to  death.  We  know  of  sainted  invalids. 
But  these  cases  which  move  us  so  deeply  to  reverent  ad- 
miration are  the  ones  in  which  the  nervous  system  in  its 
higher  parts  has  been  left  relatively  unscathed.  When  it 
is  disordered  we  can  no  more  expect  an  exhibition  of  fine 
and  strong  character  than  we  can  expect  beautiful  music 
from  an  instrument  which  is  altogether  out  of  tune.  The 
neurasthenic  is  not  his  best  self. 


NEURASTHENIA  211 

When  this  is  said,  the  question  arises,  Is  there  a  sharp 
hne  between  the  temporary  warping  of  disposition  that 
we  see  in  the  neurasthenic  and  the  irresponsibility  of  def- 
inite insanity?  A  recent  writer  has  set  a  standard  which 
is  an  attractive  one  if  we  can  be  wise  enough  to  apply  it 
rightly.  It  is  this:  The  neurasthenic  differs  from  the 
psychasthenic,  as  we  may  call  the  graver  defective,  in  the 
fact  that  he  fabricates  nothing,  but  merely  exaggerates  and 
distorts.  There  is  some  foundation  for  all  his  complaints. 
He  is  not  insane  until  he  is  in  touch  with  things  which 
have  no  existence  for  other  people.  Fortunately,  in  the 
vast  majority  of  cases,  he  is  destined  to  recover  his  poise 
and  not  to  cross  the  sinister  boundary. 

There  are  few  things  more  difficult  than  to  deal 
humanely  and  yet  firmly  and  consistently  with  neuras- 
thenia. A  tolerant  and  even  mind  is  called  forgone  that 
shall  possess  all  the  temperance  and  perspective  which  for 
the  time  being  are  so  sadly  wanting  in  the  patient.  The 
most  cruel  anguish  which  must  be  endured  is  in  experien- 
cing the  enfeeblement  of  affection  which  has  overtaken  the 
stricken  husband  or  wife.  Cutting  words  from  the  once 
loyal  companion,  bitterness  that  would  never  be  exhibited 
to  a  stranger,  must  be  borne  without  remonstrance.  The 
superiority  of  the  sanitarium  to  the  home  in  most  cases 
may  be  traced  to  the  usual  failure  to  live  up  to  such  exac- 
tions. In  the  institution  some  restraint  is  imposed  upon 
the  patient  by  the  strangeness  of  his  contacts,  while  the 
trained  attendants  maintain  a  uniform  attitude  instead  of 
alternating  between  caresses  and  angry  argument. 

It  must  not  be  forgotten  that  the  suffering  described  by 
the  neurasthenic  is  as  real  as  any  that  life  brings.  It 
merits  sympathy.  Yet  the  free  expression  of  much 
sympathy  sinks  the  victim  in  deeper  despondency  and 
encourages  him  to  invent  new  theories  to  account  for  his 
misery.  It  also  makes  his  future  appear  darker  than  ever. 
Even  the  most  earnestly  phrased  sympathy  will  not  seem 
adequate  to  the  pity-consuming  neurasthenic.  He  remains 
skeptical  as  to  the  possibility  that  anyone  can  really  appre- 


21J      THE    NERVOUS    SYSTEM    AND    ITS    CONSERVATION 

c'iate  his  woe.  He  is  likely  to  wish  that  his  friend  might 
feel  just  what  he  feels,  showing  in  this  the  marked  con- 
trast between  his  own  state  and  that  of  the  sufferer  with 
rheumatism  or  tuberculosis,  who  is  glatl  that  others  are 
well  if  he  cannot  be. 

The  studied  withholding  of  sympathy  from  neuras- 
thenics has  often  had  remarkable  results.  It  is  doubtle.ss 
practised  in  many  sanitariums,  and  there  is  one  institution 
in  particular  in  which  it  is  a  chief  measure  of  treatment. 
The  broken-down  business  man  who  comes  to  this  resort 
does  not  wait  long  before  he  attempts  to  set  forth  his  tale 
of  hopeless  suffering,  but  each  attendant  cuts  short  his 
expatiating  with  brusque  or  jocular  rejoinders.  The 
spirit  of  the  neurasthenic  is  deeply  wounded  and,  at  first, 
his  self-pity  is  intensified.  Perhaps  he  casts  himself  upon 
his  bed  and  weeps  in  his  desolation,  turning  his  face  to  the 
wall  like  the  undisciplined  Hebrew  king. 

If  we  bear  in  mind  that  the  central  fact  in  neurasthenia 
is  excess  of  nervous  activity,  we  shall  foresee  that  correc- 
tion must  come  from  inhibition.  Now,  one  of  the  first 
steps  toward  the  attainment  of  self-control  is  taken  when 
the  patient  becomes  assured  that  he  cannot  obtain  the  sym- 
pathetic response  which  he  so  greatly  craves,  and  begins 
to  hold  his  tongue.  Another  reaction  which  is  sometimes 
beneficial  is  the  provocation  of  the  invalid  to  anger.  At 
the  sanitarium  referred  to,  the  harsh  attitude  maintained 
by  the  attendants  leads  readily  to  the  loss  of  temper  on  the 
part  of  the  sufferer.  If  he  forgets  himself  so  far  as  to  lay 
hands  upon  his  nurse,  he  is  vigorously  handled.  Insulted 
and  humiliated,  he  descends  to  the  uttermost  depths  after 
such  a  passage  at  arms.  But  if  the  experience  is  repeated 
at  intervals,  the  regular  habits  and  general  hygienic  con- 
duct of  the  institution  having  their  effect  in  the  mean- 
time, the  emotion  of  anger  gradually  comes  to  bring  with 
it  a  sense  of  power  instead  of  impotence.  The  return  of 
self-reliance  and  self-government  is  said  to  be  splendid  to 
witness.  If  a  day  comes  when  the  convalescent  demon- 
strates that  he  can  put  his  tormentor  out  into  the  corridor, 


NEURASTHENIA  213 

he  rejoices  with  a  hvehness  that  he  had  never  expected  to 
reaUze  again. 

Plainly,  this  systematic  piquing  of  the  nervous  invalid  to 
restore  both  the  capacity  for  inhibition  and  for  vigorous 
performance  cannot  be  practised  successfully  upon  those 
who  have  organic  disorders  as  an  important  element  of 
their  condition.  Medical  or  surgical  treatment  is  appro- 
priate in  all  such  cases.  Attractive  meals  and  acceptable 
forms  of  recreation  are  of  great  importance.  Courtney 
protests  against  the  common  error  of  sending  neuras- 
thenics into  the  country,  where  they  find  a  degree  of  stag- 
nation that  is  as  distressing  to  them  as  the  excess  of 
action  from  which  it  is  planned  to  have  them  escape. 
A  medium  condition  is  to  be  chosen,  in  which  both  the 
sense  of  pressure  and  the  sense  of  enforced  idleness  may  be 
avoided.  If  the  patient  is  willing  to  be  lazy  for  a  while, 
this  is  very  fortunate,  but  it  is  more  likely  that  he  will 
demand  some  variety  of  interests. 

Exercise  is  a  definite  need  of  the  neurasthenic,  but  it  is 
desirable  that  it  shall  be  interesting  and  not  merely  mechan- 
ical. Courtney  recommends  hunting,  because  it  is  so  well 
calculated  to  take  one  out  of  self  and  fix  the  attention  on 
the  world  outside.  The  more  the  mind  can  be  made  to  con- 
cern itself  with  the  messages  of  the  special  sense  organs, 
the  less  it  can  dwell  upon  the  misbehavior  of  the  body. 
Much  may  be  said  in  favor  of  walking  in  mild  or  incipient 
cases.  Long  tramps  in  the  country  are  not  quite  so  refresh- 
ing as  they  were  before  the  automobiles  filled  the  roads 
with  dust  and  stenches  and  woke  the  echoes  with  their 
raucous  and  insulting  horns,  but  it  is  still  possible  to 
choose  routes  over  byways  which  are  rarely  invaded  by 
motor  cars.  The  most  stimulating  element  in  a  walk  is 
novelty.  The  country  should  not  be  well  known  to  the 
walker.  He  will  then  have  a  delightful  series  of  surprises 
as  the  unexpected  landscapes  open  to  his  view,  broad 
prospects  from  the  hill-tops  and  glimpses  of  rushing  brooks 
in  shaded  valleys. 

A  vigorous  walk  of  a  hundred  miles  in  four  days  taken 


214      THE    XEKVOUS    SYSTEM    AND    ITS    CU^■SER^■AT10X 

when  one  has  recojiiiized  signs  of  nervous  fatigue  will  often 
exert  a  prolonged  and  favorable  influence  on  one's  condi- 
tion. It  is  hard  to  find  a  congenial  companion  for  such  an 
excursion,  and  on  some  accounts  it  is  not  a  bad  plan  to  go 
alone.  There  can  then  be  no  clash  of  wishes,  and  it  may  be 
profoundly  restful  not  to  be  obliged  to  talk.  The  gentle 
mental  stirring  which  attends  the  uncertainty  regarding 
the  course  and  ending  of  each  stage  is  exceedingly  whole- 
some. Equalh^  so  on  the  phj'^sical  side  is  the  profuse  out- 
puring  of  perspiration  and  the  compensator}-  water  drink- 
ing. Village  hotels  rather  than  farmhouses  are  to  be 
recommended  as  stopping-places.  They  do  not  impose 
the  obligation  of  sociability  upon  the  tired  wayfarer  and 
they  usually  offer  him  the  luxury-  of  a  hot  bath. 

Sea- voyages  are  often  beneficial  to  those  who  lack  vigor 
for  more  active  recreation.  There  is  hardly  another  situa- 
tion in  which  individual  responsibility  is  so  successfully 
annulled  and  one's  fortunes  so  absolutely  committed  to 
others.  But  the  life  on  shipboard  does  not  appeal  to  all 
temperaments.  The  scenic  aspect  of  the  ocean  presents 
abundant  variety  to  the  observer  who  loves  it,  but  another 
finds  it  monotonous. 

We  have  previously  maintained  that  intellectual  inter- 
ests ought  to  make  for  stability  of  nervous  organization. 
It  should  now  be  clear  that  what  the  neurasthenic  most 
lacks  is  sense  of  proportion.  His  own  concerns  are  mag- 
nified undul}^  and  the  present  circumstances  are  allowed 
too  greatly  to  outweigh  those  which  have  obtained  in  the 
past  and  may  return  in  the  future.  It  is  a  mark  of  mental 
soundness  to  be  able  to  overrule  such  a  tendency.  If  a 
man  passing  through  temporary  troubles  can  hve  over  the 
happier  events  of  an  earlier  time,  and  can  realize  the  prob- 
ability that  they  will  again  be  realized,  he  is  sustained  by 
these  ties  as  the  Alpine  tourist  is  held  safe  by  the  other 
members  of  his  party. 

Some  knowledge  of  science  is  well  calculated  to  fortify 
one  against  egotism.  It  is  hard  to  see  how  anyone  who 
possesses  the  scientist's  grasp  of  time  and  space  can  fall 


NEURASTHENIA  215 

into  the  habit  of  overemphasizing  his  own  importance  to 
the  universe.  Yet  he  should  not  think  meanly  of  himself. 
The  poise  that  springs  from  having  a  scientific  perspective 
is  compounded  of  belief  in  the  value  of  individual  effort 
and  the  restful  conviction  that  when  such  effort  flags 
through  weariness  the  creative  currents  of  nature  flow  on 
in  other  channels. 

This  comes  very  near  to  religion,  at  least  to  Matthew 
Arnold's  faith  in  "a  power  not  ourselves  that  makes  for 
righteousness."  This  has  been  called  the  irreducible 
minimum  of  religion.  For  the  vast  majority  of  mankind 
the  philosophic  belief  is  not  a  commanding  motive  until 
it  is  warmed  with  an  infusion  of  devotion  and  personality. 
But  whatever  the  clothing  of  the  central  idea,  its  inesti- 
mable power  to  sustain  health  and  efficiency  has  been  rec- 
ognized in  every  age.  At  the  present  time  it  is  familiarly 
associated  with  Christian  Science. 

To  an  outsider  the  leadership  of  this  cult  appears 
domineering  and  mercenary.  The  adherents  seem  utterly 
inconsistent.  We  see  them  yielding  to  hunger,  fatigue, 
cold,  and  heat.  They  grow  old,  sicken,  and  die.  Yet 
we  may  not  doubt  that  they  maintain  on  their  course 
an  exceptionally  high  average  condition.  If  a  touch  of 
fanaticism  encourages  them  in  the  belief  that  the  same 
achievements  are  denied  to  those  who  hold  other  creeds, 
we  can  understand  that  this  very  defect  is  a  source  of 
positiveness  and  conviction.  Bigotry  is  better  for  man 
than  indifference,  though  we  may  well  seek  to  combine 
earnestness  with  generosity  and  tolerance. 


CHAPTER  XVIII 

SOME   MATTERS   OF   GENERAL  HYGIENE 

It  will  be  well  to  supplement  the  suggestions  already 
made  with  some  others  that  do  not  readily  find  their  place 
under  the  titles  of  previous  chapters.  Emphasis  has  been 
placed  on  the  fact  that  all  that  favors  the  well-being  of  the 
nervous  system  goes  to  support  the  general  health.  But 
there  is  danger  of  a  one-sided  view  if  the  opposite  asser- 
tion is  not  admitted ;  namely,  that  all  that  ministers  to  the 
other  systems  helps  to  preserve  the  nervous  mechanism. 

Five  heads  may  be  suggested  which  shall  fairly  cover 
the  requirements  of  hygiene.  These  are:  (1)  A  sound  in- 
heritance, (2)  successful  nutrition,  (3)  suitably  varied 
activity  in  all  departments  of  organization,  (4)  rest  prop- 
erly adjusted  to  the  foregoing,  and  (5)  a  wholesome  en- 
vironment. When  we  consider  the  last-named  subject  we 
find  that  it  covers  some  matters  for  which  the  individual 
is  responsible  and  some  which  rest  upon  the  community. 
Sufficient  attention  has  already  been  bestowed  upon  some 
of  these  topics;  others  may  now  be  granted  a  little  space. 

The  teachings  of  modern  science  concerning  heredity 
may  have  confused  the  thinking  of  some  intelligent 
readers,  and  it  may  be  worth  while  to  venture  a  few  com- 
ments. The  widespread  interest  in  eugenics  makes  people 
who  are  intellectually  honest  anxious  to  be  rightly  in- 
formed as  to  how  far  they  can  influence  the  physical  and 
mental  estate  of  their  children.  The  average  man  will 
probably  be  found  to  have  a  very  definite  behef  in  this 
connection.  He  thinks  that  his  moral  victories  secure 
stamina  in  the  offspring,  and  that  his  lapses  weaken  his 
progeny.  He  is  likely  to  think  that  athletic  training  on 
his  part  will  endow  his  son  with  a  superior  musculature. 
21Q 


SOME    MATTERS    OF    GENERAL    HYGIENE  217 

Similarly,  he  may  assume  that  scholarly  achievements  of 
his  own  will  make  similar  attainments  easier  for  his 
children. 

When  a  man  holding  views  like  these  first  hears  that 
scientists  generally  deny  "the  inheritance  of  acquired 
characters"  he  is  likely  to  feel  that  his  moral  responsibil- 
ity has  been  gravely  impaired.  The  immediate  impression 
is  that  conduct  is  without  significance  in  heredity,  and  that 
a  very  strong  and  noble  motive  for  self-restraint  has  been 
abolished.  Reflection  will  convince  one  that  such  im- 
pressions are  not  wholly  warranted.  One's  obUgations  are 
scarcely  impaired. 

In  the  first  place,  there  are  at  least  two  consequences  of 
transgression  which  are  still  believed  to  pass  on  from  father 
to  son.  Syphihs  is  one  of  these.  The  other  is  the  complex 
of  effects  induced  by  alcoholism.  Therefore,  deterrents 
from  the  two  commonest  forms  of  intemperance  remain 
in  full  force.  Gonorrhea  is  not  strictly  inherited,  but  the 
peril  of  infection  at  birth  and  the  inclusion  of  the  wife  in 
the  calamity  leave  every  possible  ground  for  continence 
unshaken. 

It  may  now  be  pointed  out  that  in  matters  less  specific 
than  these  the  individual  may  still  have  reason  to  consider 
carefully  what  manner  of  hfe  he  has  led  when  he  con- 
templates parenthood.  His  acts  may  not  have  modified 
the  stock,  but  we  now  regard  them  as  illustrating  its 
properties.  These  properties  are  regarded  as  having 
great  stability.  The  son  resembles  the  father  not  because 
of  certain  acts  which  the  father  performed,  but  because 
the  inheritance  common  to  both  makes  them  likely  to  behave 
in  a  similar  way  under  similar  circumstances.  Some  one 
has  expressed  the  fact  picturesquely  by  saying  that  "the 
son  is  not  a  chip  of  the  old  block,  but  father  and  son  are 
both  chips  of  the  same  old  block"— the  immemorial 
ancestry  which  they  share. 

This  being  the  case,  a  man  reviewing  his  career  and  hav- 
ing in  mind  the  probable  future  of  his  children  may  reason 
somewhat  as  follows:  "My  indulgences  and  my  denials 


218      THE    NERVOUS  SYSTEM    AND    ITS    CONSERVATION 

have  scarcely  aft'ected  the  capacities  of  the  stock.  But 
my  mdulgences  have  exhibited  its  inherent  weaknesses  and 
my  self-restraint  has  shown  its  streng:th.  My  failures 
are  ominous  and  my  victories  reassurin"-,  for  the  like  are 
to  be  expected  in  the  life  of  my  son."  The  ^rave  and  final 
question  is  whether  the  stock  ought,  on  the  whole,  to  be 
perpetuated.  This  is  comphcated  by  the  consideration 
that  the  son  will  owe  half  his  inheritance  to  the  mother. 
"He  is  his  father's  half-])rother  by  a  different  mother." 
While  it  is  fair  to  give  due  weight  to  this  fact,  it  is  hkely 
that  many  men  have  trusted  too  freely  to  the  maternal 
stock  to  neutralize  their  shortcomings.^ 

The  data  of  eugenics  are  easily  subjected  to  ridicule, 
while,  at  the  other  extreme,  too  much  may  be  expected 
from  the  new  science.  We  can  already  see  that  at  least 
one  valuable  service  may  be  rendered  by  it.  The  workers 
in  this  field  are  showing  that  hereditary  defects  are  of  two 
classes,  those  due  to  lack  and  those  due  to  positive  features 
of  the  germ  plasm.  A  lack  can  be  made  good  by  proper 
mating;  a  positive  property  will  taint  the  offspring  what- 
ever partner  may  have  been  secured,  and  so  can  never  be 
neutralized.  It  is  agreeable  to  find  that  the  majority  of 
abnormalities  are  deficiencies,  and  theoreticalh^  can  be 
bred  out  of  the  race  instead  of  being  allowed  to  die  out. 
Practically,  however,  the  strong  and  efficient  can  hardly 
be  expected  to  forego  mating  with  their  equals  to  redeem 
the  weaker  stocks. 

Since  reference  has  been  made  above  to  the  damage 
done  by  alcohol,  we  may  pursue  the  subject  further  and 
say  something  of  its  individual  as  well  as  its  hereditary 
results.  Two  opjwsing  views  of  the  general  problem  are 
maintained.  Most  writers  assume  that  alcohol  is  a  chief 
cause  of  degeneracy.  On  the  other  hand,  it  is  ingeniously 
maintained  that  the  indulgence  is  as  much  a  sign  as  a 
cause  of  the  conditions  with  which  it  is  associated.  Accord- 
ing to  this  conception,  a  drunkard  is  a  man  who  would 

1  Jordan,  "The  Heredity  of  Richard  Roe,"  The  American  Uni- 
tarian Association,  Boston,  1911. 


SOME    MATTKIiS    OF    GENERAL    HYGIENE  219 

have>  been  a  worthless  fellow  even  if  he  had  never  discov- 
ered the  consolations  of  liquor.  This  we  can  readily 
grant  for  certain  cases,  but  we  can  think  of  others  where 
we  feel  sure  that  nothing  but  alcoholic  intemperance  has 
stood  in  the  way  of  useful  or  even  briUiant  attainment. 

One  thing  which  we  do  not  much  like  to  remember  is 
that  none  of  us  are  many  generations  removed  from  ances- 
tors who  were  frequently  intoxicated.  Only  the  Mahome- 
tan can  claim  that  his  case  is  otherwise.  Reid  Hunt,  com- 
paring the  toxicity  of  grain  alcohol  and  wood  alcohol  as 
determined  upon  the  lower  animals,  found  that  while 
wood  alcohol  is  more  poisonous  than  the  other  the  differ- 
ence is  much  less  than  for  man.  His  suggestion  is  that  the 
human  race  is  habituated  to  grain  alcohol  by  ages  of  drink- 
ing. It  has  never  gained  any  such  tolerance  for  wood 
alcohol  largely  because  it  has  not  often  employed  it  as  a 
beverage. 

Keeping  the  welfare  of  the  nervous  system  in  the  fore- 
ground, let  us  consider  the  action  of  alcohol  as  experienced 
by  those  who  take  it  very  moderately.  It  is  popularly 
held  to  be  a  stimulant,  and  the  claim  has  a  measure  of 
scientific  support.  But  most  students  emphasize  its  de- 
pressant property,  pointing  out — what  has  been  said 
elsewhere — that  to  depress  the  inhibitory  centers  is  to 
''take  off  the  brakes"  and  to  create  an  appearance  of 
stimulation.  The  most  impressive  articles  that  have  been 
written  in  defense  of  the  retention  of  alcohol  have  come 
from  writers  who  did  not  recommend  it  as  a  stimulant,  but 
as  a  means  of  promoting  mental  relaxation  and  social  ease. 
It  is  disquieting  to  the  advocate  of  total  abstinence  to 
find  that  the  great  majority  of  the  most  original  and, 
on  the  whole,  the  most  admirable  men  have  valued  alco- 
hol as  a  social  reagent.  It  begins  to  seem  as  though  a 
reaction  were  setting  in,  but  it  will  evidently  be  a  long  time 
before  the  representative  gatherings  of  leaders  in  poUtics, 
letters,  and  even  in  education  will  forego  their  wines 
without  complaint. 

The    temperamental    change    induced    by   alcohol   in 


220    THi:  xKiivors  system  and  its  coxsiohvation 

moderate  (luantities  is  hij^lily  chanictcristic.  It  iiui}'  be 
described  as  intellectual  myopia,  a  condition  in  which  all 
that  is  near  at  hand — the  present  company  and  the  inter- 
ests of  the  hour — will  be  found  dominant,  and  all  that  is 
remote  from  these  will  tend  to  be  excluded.  Thus,  the 
cares  that  weighed  upon  the  banqueter  before  he  came  to 
the  feast  and  the  problems  he  must  face  next  morning  are 
forgotten.  We  have  insisted  that  this  detachment  is  most 
desirable  and  hygienic.  But  the  ideal  is  to  compass  it  at 
will  without  the  employment  of  a  chemical  artifice.  One 
who  can  relinquish  care  as  a  voluntary  act  can  take  it  up 
again  promptly  and  earnestly.  The  banishment  of  obliga- 
tion by  alcohol  does  not  permit  the  same  decisive  resump- 
tion of  responsibilit3^  It  is  well  for  the  man  who  is  head 
of  a  family,  when  he  reviews  some  convivial  occasion,  to 
ask  himself  whether  the  wife  and  children  at  home  did  not 
recede  farther  from  the  forefront  of  his  consciousness  than 
he  would  have  chosen  to  have  them.  Perhaps  the  bachelor 
need  not  be  so  exacting  in  his  introspective  judgment. 

It  seems  wellnigh  impossible  to  write  without  bias  of  the 
social  use  of  alcohol.  Those  who  uphold  it  charge  their 
opponents  with  a  want  of  charity  and  with  a  disposition 
to  demand  needless  renunciations  of  pleasure.  They  would 
probably  assert  that  the  tj^pical  moderate  drinker  is  a 
kindlier  man  than  the  typical  abstainer  and  that  he  is 
not  less  efficient.  To  be  quite  just  to  those  who  maintain 
this  position  one  should  read  the  pleas  of  such  writers  as 
Holmes,  Mlinsterberg,  and  Heinemann.^ 

If  it  is  a  difficult  matter  to  pass  judgment  upon  those 
who  use  alcohol,  what  shall  be  said  of  caffein,  the  active 
principle  of  tea  and  coffee?  This  is  an  agent  which  we 
sometimes  hear  unsparinglj'-  condemned,  but  most  vigor- 
ously by  those  who   have   substitutes   to  offer.     Many 

1  Holmes,  "The  Autocrat  of  the  Breakfast  Table,"  Riverside 
Edition,  Houghton,  Mifflin  &  Co.,  Boston,  p.  1S7  et  seq.  Miinster- 
berg,  "American  Problems  from  the  Point  of  View  of  a  Psychol- 
ogist," MofTat,  Yard  &  Co.,  New  York,  1910.  Heinemann,  "The 
Rule  of  Not  Too  Much,"  Chicago,  1912.  For  counter-arguments, 
see  Crooker,  "Shall  I  Drink?"  The  Pilgrim  Press,  Boston,  1914. 


SOME    MATTERS    OF    GENERAL    HYGIENE  221 

experimental  studies  have  consistently  shown  that  caffein 
is  a  true  stimulant,  actually  increasing  the  capacity  for 
muscular  and  mental  work.  The  advisabihty  of  resorting 
to  a  stimulant  must  depend  largely  upon  the  extent  of  the 
after-effect  and  upon  possible  cumulative  injury. 

A  most  painstaking  investigation  of  the  properties  of 
caffein  was  reported  recently  by  Hollingworth.^  It  was 
conducted  upon  a  considerable  scale,  a  staff  of  7  trained 
workers  gathering  data  from  16  subjects  (of  whom  10  were 
men  and  6  women).  In  all  trials  of  this  kind  it  is  neces- 
sary to  keep  the  subjects  in  ignorance  of  the  times  at  which 
they  receive  the  drug  to  be  tested.  HoUingworth  gave 
them  at  intervals  gelatin  capsules  many  of  which  were 
blanks,  while  others  contained  measured  doses  of  caffein. 
The  heaviest  dose  equalled  the  quantity  in  two  large  cups 
of  coffee.  Ingenious  tests  were  made  as  a  matter  of  daily 
routine,  whether  the  caffein  was  given  or  not.  Speed, 
dexterity,  discrimination,  and  mental  alertness  were 
observed. 

The  results  of  the  research  were  almost  entirely  favor- 
able to  caffein.  Gains  were  recorded  in  all  the  capacities 
investigated.  The  tests  made  with  the  typewriter  were 
of  the  most  practical  interest.  When  caffein  had  been 
received  by  the  worker  the  copying  was  accomplished 
somewhat  more  rapidly  and  with  fewer  errors  than  at 
other  times.  Moreover,  when  mistakes  were  made,  they 
were  more  often  recognized  on  the  instant.  It  is  instruc- 
tive to  compare  these  facts  with  those  that  have  been 
secured  with  alcohol.  Both  alcohol  and  caffein  probably 
inspire  the  user  with  confidence  in  his  ability  to  do  his  best. 
But  there  is  a  divergence  in  the  actual  performance, 
alcohol  failing  to  give  the  promised  reinforcement,  and 
caffein  confirming  the  subjective  impression  quite  deci- 
sively. 

We  naturally  assume  that  a  period  of  stimulation  will 
be  followed  by  one  of  corresponding  depression,  as  the 

^  "Archives  of  Psychology,"  The  Science  Press,  New  York, 
April,  1912. 


222      THE    NERVOUS    SYSTEM    AND    ITS    CONSKKVATION 

trough  of  a  wave  follows  the  crest.  HoUingworth  has 
failed  to  find  evidence  of  any  such  reaction.  Nothing  in 
the  report  is  more  unexpected  or  more  important  if  it  shall 
be  sustained.  If  it  is  possible  to  enhance  working  power 
and  not  entail  any  extra  fatigue,  we  must  conclude  that  the 
part  played  by  the  stimulant  may  be  quite  innocent  and 
desirable.  Several  years  ago  a  wise  teacher  suggested 
that  a  whip  is  appropriate  for  the  lazy,  but  not  for  the 
tired,  horse.^ 

In  spite  of  HoUingworth's  impressive  findings,  it  would 
be  unsafe  to  conclude  that  all  people  can  advantageously 
use  tea  and  coffee.  Many  exceptions  are  apparent.  Even 
among  the  members  of  HoUingworth's  squad  the  larger 
doses  caused  some  feverish  conditions,  headache,  and 
sleeplessness.  If  such  reactions  were  markcfl  and  long 
continued,  there  can  be  no  doubt  that  the  favorable  effects 
of  caffein  would  soon  be  exchanged  for  detrimental  ones. 
Only  three  or  four  of  the  subjects  were  non-users  of 
caffein  before  the  experimental  period.  It  is  probable 
that  there  are  a  good  many  abstainers  from  coffee  who 
have  learned  b}^  disagreeable  experience  that  they  must 
do  mth'out  it. 

While  we  may  not  condemn  in  a  sweeping  fashion  the 
taking  of  caffein,  nor  even  the  guarded  indulgence  in 
alcohol,  there  is  no  room  for  two  opinions  regarding  the 
dangers  of  more  active  drugs.  All  use  of  morphin,  cocain, 
and  their  congeners  is  perilous.  Temperance  in  their 
employment  is  conceivable,  but  seems  scarcely  ever  to  be 
realized.  The  tendency  to  increase  the  dosage  is  almost 
irresistible.  There  is  hardly  a  spectacle  so  tragic  as  that 
of  the  drug  victim,  steadily  deteriorating  in  character,  until 
his  moral  cowardice,  dishonesty,  and  lack  of  self-respect 
are  incredible  to  the  members  of  his  family.  Some  one 
has  said  that  "the  drunkard  turns  night  into  day  and  the 
morphinist  turns  day  into  night."  The  influence  of  cocain 
seems  to  resemble  that  of  alcohol  rather  more  than  that  of 

'  Hough  and  Sedgwick,  "The  Human  Mechanism,"  Ginn  &  Co., 
Boston,  1906,  chap.  xx. 


SOME    MATTERS    OP    GENERAL    HYGIENE  223 

morphin;  it  leads  to  reckless  and  violent  crime.  There  is 
a  popular  impression  that  the  habit-forming  alkaloids 
produce  delightful  subjective  states.  This  seems  rarely 
to  be  the  case  after  the  first  foolish  ventures;  the  most  that 
the  unhappy  wretch  reports  later  is  that  the  drug  relieves 
— and  often  incompletely — the  misery  of  abstinence. 

A  final  word  may  be  added  concerning  the  attitude  which 
we  should  maintain  toward  medicine  and  the  medical  pro- 
fession. Physicians  were  once  held  in  high  respect  by  all 
civilized  people.  At  the  present  time,  when  the  attain- 
ments and  principles  of  the  profession  merit,  far  more  than 
ever  before,  popular  esteem  and  admiration,  a  hostile  and 
skeptical  spirit  is  often  manifested.  Several  causes  for  this 
are  evident.  The  fact  that  drugs  are  less  relied  on  to 
remedy  diseased  conditions  than  was  formerly  the  case 
has  encouraged  the  hasty  conclusion  that  they  have  no 
value  at  all.  Errant  schools,  using  pecuhar  therapeutic 
methods,  have  fiercely  attacked  the  main  body  of  prac- 
titioners. Patients  who  have  been  benefited  by  these 
special  measures  have  joined  heartily  in  denying  the  virtue 
of  other  kinds  of  treatment.  Psychotherapy  has  led  to  the 
same  reaction  in  spite  of  the  broad  views  urged  by  its 
ablest  exponents.  Certain  periodicals  have  made  inces- 
sant, mahcious  attacks  upon  the  profession,  charging 
mercenary  aims,  unwarranted  experimentation  upon  hu- 
man subjects,  and  failure  to  effect  cures.  It  is  amusing 
— even  while  it  is  irritating — to  note  that  those  who  write 
such  articles  charge  the  physician  with  being  unwilHng  to 
adopt  new  methods,  and  in  the  next  paragraph  cry  out 
against  his  innovations.  The  dignified  silence  main- 
tained by  medical  men  in  the  face  of  these  attacks  is  not 
properly  appreciated  by  a  thoughtless  public. 

When  it  is  suggested  that  physicians  and  surgeons  ask 
excessive  fees  there  are  two  or  three  reflections  that  should 
modify  judgment.  It  is  a  trite  saying  that  restoration  to 
health  has  a  value  not  easily  expressed  in  money.  Second, 
we  should  consider  the  investment  of  time,  strength, 
and  means  which  has  equipped  the  doctor  for  his  respon- 


224      THE    XKHVOrS    8YSTi:.M    AXD    ITS    CONSERVATION 

sible  service.  Third — and  this  is  often  overlooked — it  is 
the  generous  payments  of  those  who  can  afford  them  which 
make  it  possible  for  the  practitioner  to  give  his  best  skill 
freely  to  the  poor. 

Too  many  intelligent  people  have  failed  to  read  of  the 
achievements  of  medical  science.  It  is  only  when  the 
former  insecurity  of  life  is  contrasted  with  its  present 
conservation  that  our  indebtedness  to  the  profession  is 
realized.  The  stories  of  the  conquest  of  small-pox  and 
yellow  fever  are  among  the  most  thrilling  that  can  be 
found  in  human  annals.  The  discovery  of  the  chief 
methods  of  anesthesia  and  of  the  way  to  avoid  surgical 
infection — these  have  almost  an  equal  power  to  grip  \hc 
reader.  A  little  acquaintance  with  the  literature  of 
seventy-five  years  ago  suffices  to  make  one  realize  the 
horror  of  epidemics,  particularly  of  yellow  fever  and 
cholera.  Typhus  fever,  which  once  ravaged  the  steerages 
of  emigrant  ships,  has  become  a  rare  and  curious  disease. 
Pessimists  often  lay  stress  upon  the  increasing  prominence 
of  certain  causes  of  death.  They  forget  that  since  man  is 
mortal,  the  individuals  who  escape  one  malady  must  later 
be  counted  among  the  victims  of  another.  The  happy 
fact  is  that  they  have  lived  through  longer,  more  vigorous, 
and  more  rewarding  lives. 


INDEX 


Accelerators,  cardiac,  117 
Accomplishments,  54 
Adjusters,  18,  33,  52 
Adrenal  bodies,  92,  109,  170-172 
Afferent  paths,  75-82,  99,  143 

type  of  neuron,  31,  32,  78,  79 
Age,  156,  157,  181 
Alcohol,  217-220 
Alimentary  canal,  125,  208 
AU-or-none  law,  90 
Amputation,  45 
Anemia,  194 

theory  of  sleep,  175-177 
Anesthesia,  196 
Anger,  168,  212 
Animals,    decerebrate,    129-133, 

174 
Ant,  47 

Antagonistic  muscles,  94 
Anticipation,  159,  160 
Aphasia,  motor,  147-149 
Association  areas,  150,  151 

fibers,  151 
Associative  memory,  128,  129 
Astigmatism,  195,  196 
Ataxia,  99 
Auditory  area,  145 

nerve,  73,  81 
Auto-intoxication,  193,  194,  209 
Automatic  property,  20 
Autonomic  system,  114-126,  175 
in  emotion,  170-172 
in  neurasthenia,  207-210 
Axis  of  nervous  system,  66,  67 
Axis-cyUnder  or  axon,  26 
15 


Bell's  law,  62 

Brain,  circulation  in,  175 

frog's,  60-65 

gray  matter  in,  70 

rabbit's,  65-67 

ventricles  of,  64 
Breathing,  99,  100 
Burnett  on  decerebrate  frogs,  130, 

note 

CAFrEiN,  220-222 

Camis  on  reflexes,  93 

Cannon    on    emotion,    165-167, 
170,  171 

Cardiac  accelerators,  117 
nerves,  116-118 

Cavities  of  central  nervous  sys- 
tem, 62-64 

CeU  theory,  22 

Cells,  22-24 

Cerebellum,  65,  68,  96-99,  128 

Cerebral  hemispheres.     See  Cere- 
brum. 

Cerebrospinal  fluid,  61 

Cerebrum,  64,  70,  88,  127-155 
lobes  of,  71 

Chiasma,  73 

Chorda  tympani,  119 

Christian  Science,  215 

Cii'culation  in  brain,  175 

City  Ufe,  167 

Cold,  sensation  of,  78 

Concentration   and   detachment, 
158 

Conduction,  25,  79 

225 


22() 


INDEX 


Congestion,  121,  122 

Connective  tissue,  11 

Constipation,  209,  210 

Contractile  tissue,  12 

Convolutions,  70 

Coordination,  14,  93 

Corpora  quaclrigcmina,  66 

Corpus  callosum,  70 

Cortex,  70,  136 

Coughing,  50 

Courtney  on  neurasthenia,  204- 

213 
Cranial  nerves,  60,  71-74 
Crile  on  unfelt  injury,  196-199 
Crura  cerebri,  69 
Cytoplasm,  24 

Dancing,  109 

Darwin's  use  of  limited  strength, 

159 
Decerebrate    animals,     129-133, 
174 

child,  132 
Degeneration,  35 
Delirium,  92 
Dendrites,  29 
Dendrons,  29 
Depth  of  sleep,  178 
Descartes  on  memorj^  136 

on  reflexes,  49 
Diaphragm,  103 
Diet,  influence  of,  112 
Dreams,  184-191 

classified,  184 

eyes  in,  190 

sensations  in,.  197 

symbolism  in,  187 

visceral  symbols  in,  187 
Drugs,  222 


EfTcctors  defined,  18 

Elbow,  42 

Electric  i)henomena,  17,  39,  171 

Ellis  on  dreams,  177,  184-191 

Emotion,  164-172 

Epilepsy,  142 

Epithelial  tissue,  12 

EquiUbrium,  81,  97 

Escape  (of  heart),  117 

Eugenics,  216-218 

Evolution    of     nervous    system, 

19 
Eye-muscles,  74 
Eyes  in  dreams,  190 
Eye-strain,  194-19t) 

Far-sight,  195 

Fatigue  and  dreams,  185-187 

general,  203-205 

neuromuscular,  101-110 

synaptic,  105 
Fatigue-products,  101,  102 
Fibers,  association,  151 

regeneration  of,  35 

secretory,  126 
Fibrils,  26,  34 
Fingers,  80 
Flatulence,  209 

Flechsig  on  association  areas,  151 
Fletcher  on  hours  of  sleep,  181 
Flourens,    pioneer    experiments, 

130,  133 
Forbes  on  fatigue,  105-107 
Foster  on  old  age,  156,  208 
Freud  on  dreams,  189 
Friction,  domestic,  200 
Frog's  nervous  system,  60-65 
Functional  and  organic  disorders, 

203 


Early  conceptions  of  nerve  ac-  i  Gage,  Phineas,  152 
tion,  37  :  Gall,  phrenologist,  134 


INDEX 


227 


Ganglia,  27,  115,  116 

of  dorsal  roots,  78 
Ganglion,  Gasserian,  80 
Genito-urinary  symptoms,  210 
Glands,  nervous  control  of,  126 
Goltz's  decerebrate  dog,  132 
Gordon  on  infant  mind,  154 
Gradation  of  muscular  responses, 

89-93 
Gravity  and  the  circulation,  123, 

124 
Gray  antl  white  matter,  26-28 

matter  in  brain,  70 
in  cord,  68 
Growth  of  muscles  with  use,  111 
Gyri,  70 

Habits,  54,  155,  156 

Hearing,  81 

Heart,  116-118,  120,  121,  208 

inhibition  of,  117 
Heredity,  192,  216-218 
Hollingworth  on  caffein,  221,  222 
Howell  on  sleep,  176,  180 
Hunt  on  alcohol,  219 
Hygiene,  155-163,  167-170,  180- 

182,  185-187,  200-202,  213-224 
Hypnotism,  rapport  of,  56 

Individual,  16,  47,  127 

Infancy,  153-155 

Inhibition,  20,  21,  157,  209.  212 

of  heart,  117 

withdrawal  resembles  stimula- 
tion, 20,  205,  219 
Inhibitory  influence  on  centers, 

104,  108 
Integration,  16 
Intelligence,  127,  146 
Intercellular  substance,  24 
Intoxication,  205 


James  on  emotion,  167,  168 

on  habits,  155,  156' 
James-Lange  theory,  164,  171 
Jordan  on  heredity,  218 

Language,  147-150 
Law,  all-or-none,  90 

BeU's,  62 
Lee  on  fatigue,  102,  204 
Lincoln's  power   of  detachment, 

158 
Lingle  on  tonus,  91 
Lobes  of  cerebrum,  71 
Localization,  133-152 
Loeb  on  locahzation,  139 
Lucas  on  muscular  action,  89-93 

Martin  et  al.  on  sensory  thresh- 
old, 162 
Medicine,  223,  224 
Medulla,  63,  128,  143 
Melius  on  the  cortex,  150 
Memory,  137,  161,  186 

associative,  128,  129 
Meninges,  61,  62 
Midbrain,  64 
Monotony,  160 
Motor  aphasia,  147-149 

areas,  138-143 

end-plates,  87, 102, 104, 112, 166 

neurons,  33,  85 
Miiller,  43,  207 
MiiUerian  principle,  44,  76 
Mimsterberg  on  free  agency  and 

mind,  141 
Muscle-fibers,  85 
Muscles,  antagonistic,  94 

eye-,  74 

Near-sight,  194,  195 
Nerve  action,  early  conceptions 
of,  37 


228 


INDEX 


Nerve,  auditory,  73,  81 

imijulscs,  37-40,  43 

olfactory,  Go,  71 
in  fish,  129 

optic,  65,  72 

trigeminal,  73,  SO 

vagus,  73 

vestibular,  81 
Nerve-centers,  53 
Nerve-fibers,  25,  26 
Nerves,  25 

cardiac,  116-118 

cranial,  60,  71-74 

spinal,  60 
Neurasthenia,  188,  203-215 

sensations  in,  206,  207 
Neurasthenic  temperament,  188, 

210 
Neiu'omuscular  fatigue,  101-110 

unit,  86,  87 
Neuron,  afferent  type,  31,  32,  78, 

79 
Neurons,  motor,  33,  85 

postganglionic,  115 

preganglionic,  115 
Neiu-opile,  34 
Newborn,  54 
Nodes  of  Kanvier,  26 
Nucleus,  24 
Nutritional  disturbances,  193 

Occupation,  199 
Olfactory  area,  145 

nerve,  65,  71 
in  fish,  129 
Optic  chiasma,  73 

nerve,  65,  72 
Orthodontia,  198 
Overwork,  199 

I^AIN,   199 

Paths  of  easy  transmission,  46 


Perikaryon,    alteration    through 
activity,  41,  197 
defined,  30 

reinforcing  function,  41 
related  to  nutrition,  34 

Phrenology,  134,  135 

Pilomotor  action,  125 

Play  and  work,  110 

Pk^tliysmograph,  179 

Pons,  ()S 

Postganglionic  nem-ons,  115 

Posture,  123,  124 

Preganglionic  neurons,  115 

Prince  on  memory,  137 

Profanity,  148 

Projection  fibers,  88,  143 

Protoplasm,  24 

Psychanalysis,  188-190 

Psychasthenia,  211 

Psychology,  16,  140 

Psychotherapy,  197,  198,  215 

Punctiform  sensibility,  77 

Putnam  on  fatigue,  205 

Rabbit's  brain,  65-67 
Ranvier,  nodes  of,  26 
Rapport  of  hjqjnotism,  56 
Reaction-time,  58 
Reading  area,  149 
Receptors,  18,  76 
Reciprocal  innervation,  95,  96 
Reflexes,  49-59,  87 

conditioned,  55 

type    of    all    nervous    action, 
139 
Regeneration  of  fibers,  35 
Religion,  163,  202,  215 
Resjjiratory  center,  100 
Restlessness,  206 
Right-handed  condition,  146 
Roots,  dorsal  and  ventral,  62 
Ruts,  46,  156 


INDEX 


229 


Sabbath,  161-163,  201,  202 
Science,  214,  215 
Sea-voyages,  214 
Secretory  fibers,  126 
Sensations,  44,  76-84,  104 

general  and  special,  83,  84 

in  dreams,  191 

in  neurastlienia,  206,  207 
Sensibility,  punctiform,  77 
Sensory  threshold,  162,  207 
Sexual  life,  189,  190,  217 
Sherrington  on  coordination,  94- 

96 
Singing,  170 
Skill,  113 
Skin,  75,  121 
Sleep,  173-183 

anemia  theory  of,  175-177 

depth  of,  178 

toxemia  theory  of,  175-177 
Smell,  81 

Speech  center,  147-150 
Spinal  cord,  60,  69,  127 
gray  matter  in,  70 
Spontaneity,  131 
Starling  on  cerebrum,  127 
Stedman  on  Lincoln,  158 
Stimuli,  17,  36,  37,  82 
Strain,  eye-,  194-196 
Sulci,  70 

Symbolism  in  dreams,  187 
Sympathetic  system,  116,  170 
Sympathy,  168,  211 

withholding  of,  212 
Synapse,  28,  33,  88 

valve  action  of,  29,  30 
Synaptic  fatigue,  105 

resistance,  46,  182 

Taste,  81 

Temperature  and  blood-flow,  121, 
208 


Thomson  on  aphasia,  148 

on  sleep,  174 
Tissues,  11-14 

connective,  11 

contractile,  12 

epithelial,  12 

nervous,  13 
Tolerance,  200 
Tonus,  55,  119 
Toxemia   theory   of   sleep,    175- 

177 
Training,  91,  110-113 
Treppe,  102 
Trigeminal  nerve,  73,  80 


Vagus  nerve,  73 
Valve  action  of  synapse,  29,  30 
Vasoconstrictors,  118 
Vasodilators,  119,  120 
Vasomotor    reactions,    55,    118- 

125,  208 
Velocity  of  nerve-impulse,  40 
Ventilation,  198,  199 
Ventricles  of  brain,  64 
Vestibular  nerve,  81 
Visceral  muscle,  114 

symbols  in  dreams,  187 
Vision,  80 

Visual  areas,  140,  144 
Vital  resistance,  123 
Voluntary  action,  53,  58,  87 


Walking,  53,  98,  213 

Waste-products  of  nerve,  39 
(and  note).     See  Fatigue. 

Wells  and  Forbes  on  electric  dis- 
turbances, 171 

Wink,  50 

Women,  dull  lives  of,  169 

Writing,  149 


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G©Asim'§   Lab®]rsiit®irj    lBaicih(giri(S)l®gj 

Laboratory  Bacteriology.  By  Fkhdbric  P.  Gorham,  A.  M., 
Associate  Professor  of  Biology,  Brown  vJniversity,  Providence. 
i2mo  of  192  pages,  illustrated.     C'oth,  $1.25  net. 

The  subjects  of  special  interest  to  scientific  students  are  the  identifica- 
tion of  bacteria  of  water,  milk,  air,  and  soil.  Professor  Gorham  has 
succeeded  in  making  his  instructions  clear  and  easily  grasped  by  the 
student.     The  text  is  illustrated. 

Science:  "  The  author  has  described  small  points  of  technic  usually 
left  for  the  student  to  learn  himself." 


Saunders'  College  Text-Books 


L'^uiik^s  EldiMdinifLi  ©f  MMitirifta©ini 

Elements  of  Nutrition.  By  Graham  Lusk,  Ph.  D.,  Professor  of 
Physiology,  Cornell  Medical  School.  Octavo  of  402  pages,  illus 
trated.     Cloth,  ^3.00  net.  Second  Edition. 

The  clear  and  practical  presentation  of  starvation,  regulation  of  tem- 
perature, the  influence  of  protein  food,  the  specific  dynamic  action 
of  food-stuffs,  the  influence  of  fat  and  carbohydrate  ingestion  and  of 
mechanical  work  render  the  work  unusually  valuable.  It  will  prove 
extremely  helpful  to  students  of  animal  dietetics  and  of  metabolism 
generally. 

Dr.  A.  P.  BrubeJcer,  Jefferson  Medical  College:  "  It  is  undoubtedly  the 
best  presentation  of  the  subject  in  English.    The  work  is  indispensable." 


ini©W(iM  §  irlnky§n©il©gy 

Physiology.  By  William  H.  Howell,  M.  D.,  Ph.  D.,  Professor 
of  Physiology,  Johns  Hopkins  University.  Octavo  of  1020  pages, 
illustrated.     Cloth,  $4.00  net.  Fijlh  Edition. 

Dr.  Howell's  work  on  human  physiology  has  been  aptly  termed  a 
"storehouse  of  physiologic  fact  and  scientific  theory."  You  will  at 
once  be  impressed  with  the  fact  that  you  are  in  touch  with  an  expe- 
rienced teacher  and  investigator. 

Prof.  G.  H.  Caldwell,  University  of  North  Dakota:  "  Of  all  the  text- 
books on  physiology  which  I  have  examined,  Howell's  is  the  best." 


B(iirg(iy  §  iniygEdsiKi 

Hygiene.  By  D.  H.  Bergey,  M.  D.,  Assistant  Professor  of  Bac- 
teriology, University  of  Pennsylvania.  Octavo  of  530  pages,  illus- 
trated.    Cloth,  %T,.oa  net.  Fourth  Edition. 

Dr.  Bergey  gives  first  place  to  ventilation,  water-supply,  sewage,  indus- 
trial and  school  hygiene,  etc.  His  long  experience  in  teaching  this  sub- 
ject has  made  him  familiar  with  teaching  needs. 

J.  N.  Hurty,  M.  D.,  Indiana  University:  "  It  is  one  of  the  best  books 
with  which  I  am  acquainted." 


Saunders'  College  Text-Books 


OTTQw^B  Cmird  ©f  IiniJMircidl 

imtiteiiiate  Care  of  the  Injuyed.  By  Albhkt  S.  Morhdw,  M.D., 
Adjunct  Professor  of  Surgery,  New  York  Polyclinic.  Octavo  of 
360  pages,  242  illustrations.     Cloth,  S2. 50  net.  Second  Edilion. 

Dr.  Morrow's  book  tells  you  just  -what  to  do  in  any  emergency,  and  it 
is  illustrated  in  such  a  practical  way  taat  the  idea  is  caught  at  once. 
There  are  chapters  on  bandaging,  practical  remedies,  first-aid  outfit, 
h>TDodermic  injections,  antiseptics  and  disinfectants,  accidents  and 
emergencies,  hemorrhages,  inflammation,  contusions  and  wounds,  burns 
and  scalds,  the  injurious  effects  of  cold,  fractures  and  dislocations, 
sprains,  removal  of  foreign  bodies  from  the  eye,  ear,  nose,  etc.,  poisons, 
and  their  antidotes.  There  is  no  book  better  adapted  to  first-aid  class 
work. 

Health :  "  Here  is  a  book  that  should  find  a  place  in  every  workshop 
and  factory  and  should  be  made  a  text-book  in  our  schools." 

A.inni(g]rn€ai!ni  Hll^iftiraiLed!  DEcitioiniaiiry 

American  Illustrated  Medical  Dictionary.  By  W.  A.  Newman 
DoRLAND,  M.  D.,  Member  of  Committee  on  Nomenclature  and 
Classification  of  Diseases,  American  Medical  Association.  Octavo 
of  1107  pages,  with  323  illustrations,  119  in  colors.  Flexible 
leather,  $4.50  net  ;  thumb  indexed,  $5.00  net.  Seventh  Edilion 

If  you  want  an  unabridged  medical  dictionary,  this  is  the  one  you 
want.  It  is  down  to  the  minute;  its  definitions  are  concise,  yet  accu- 
rate and  clear;  it  is  extremely  easy  to  consult;  it  defines  all  the  newest 
terms  in  medicine  and  the  allied  subjects;  it  is  profusely  illustrated. 
This  new  edition  alone  defines  over  s<^oo  new  terms  not  defined  in  any 
other  medical  dictionary — har  none.  There  is  no  other  medical  dic- 
tionary that  will  meet  your  needs  as  well  as  The  American  Illustrated. 
Why  not  then  get  the  best  ? 

John  B.  Murphy,  M. D.,  Northwestern  University:  "It  is  unquestion- 
ably the  best  lexicon  on  medical  topics  in  the  English  language,  and, 
with  all  that,  it  is  so  compact  for  ready  reference." 

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